This was requested as I recently completed watching Season 1 of Star vs FOE along with a friend.
I want to quickly explain the way I rate everything on a 5 point basis:
5/5: Very likely my favorite in it's genre. Potentially my favorite in the medium. Something I greatly enjoy, that has great intellectual and emotional resonance with me. I would view this again and again by myself. I would style my own work after the ideas in it. If someone loves this work, I would be instantly companions with them in some way.
4/5: I really enjoyed the work. Something I might recommend to people and would view again with other people or after a long time. Has at least a few elements that I absolutely loved and might try to replicate. If someone loves this work, I will chatter with them about it and have fun.
3/5: I thought it was enjoyable enough. It fills the time and serves it's purpose though I wouldn't go out of my way to call myself a fan or go to defend it. Glad I viewed it once but probably won't again. If someone loves this work, I will see why but I won't have much to say.
2/5: Generally meh. I didn't find it very entertaining or it has some good elements but they are too diluted for my to really enjoy. I kinda regret using the time on it, though I won't argue with someone who likes it or whatever. If someone loves this work, I will be a bit confused why, but will leave them to their enjoyment.
1/5: Actively angers, annoys, or offends me. A work that I actively avoid talking or thinking about when possible. A work I will only view if I have to. If someone loves this work, I will try my best to stay quiet so as not to show my disdain for it.
I judge everything by this metric, although primarily art. I also judge sub-sections by these metrics. So let me analyze various sections. In particular, I judge 5 sections in particular: Characters, Plots, Aesthetic (including World when applicable), Mood, and Genre.
The two primary protagonists of Star versus The Forces of Evil are Star Butterfly and Marco. The Standard Magical Girl Formula for Female and Male Leads involve a Girl with one particular Virtue and her character being backwards built to emphasize the point, and the Male acting as the counterpoint by being a contrast.
Star Butterfly's particular virtue seems to be her dynamism, as it were. Star is introduced as a fun, extroverted girl who shakes up and disrupts broken systems. She brings excitement and enjoyment to other mundane or dark situations. Marco act as her counterpoint, a calm, rational, vaguely introverted boy who is proficient in a discipline form of combat (Karate) as opposed to Star's more emotion-based magic. I found them an enjoyable pair of protagonists....
The biggest fault of Star vs. FOE so far is where most MG Shows falter...which is villains. he primary villain most of the season is Ludo who is entirely a joke, and not one I found funny. Most of his henchmen I didn't find particularly memorable save for Buff Frog who has a substantial and enjoyable part of the climax and has a small character arc within the last set of episodes. Near the end Ludo is temporarily replaced as Villain by Toffee. Toffee was a marked improvement as a villain, having drastically more menace, an interesting gimmick (hating magic), and a slightly more interesting arsenal (increased intellect and regeneration). That said he was only main villain briefly, and more could have been done with his character as very little is shared of his backstory and while his personality is a dimension ahead of Ludo's, it's still 2 dimensional really.
The minor characters are for the most part enjoyable and make for a well-defined world. Marco's Parents are fun to watch and it's good to see a marriage on screen that is still clearly loving, passionate, and romantic, especially considering the one other on-screen marriage is Star's parents. Speaking of which, Star's parents are surprisingly developed. With few exceptions, the parents of the main Magical Girl tend to be either A: Comically Perfect, B: Never mentioned. While I didn't like the introduction to Star's parents which them made out to be 1-dimensional archetypes of a manipulative angry overly strict mother and a bumbling wild father (the classical parents dynamic), they showed more character then that eventually. Particularly in the last episode. (Star: "You're mad at me." Star's Mother: "I'm just glad you're safe." DAWWWWWWWWWW, also total Chibiusa and Setsuna flashback.). Jackie is a cute love interest for Marco, though we don't really know much about her. Brittany, I'll be honest I'm pretty tired of the rich b*tch stereotype for personal reasons. Alfonzo and Ferguson are just sort of there. I'll be honest, I find the Earth-based characters less interesting. Though the angry teacher figure Miss Skullnick, is surprisingly in-depth. (The American Magical Girl is more respectful to the Sensei character. Go figure). Star's got a Magical Friend called "Flying Princess Pony Head", who is basically exactly what the name sounds like. I was pleasantly surprised that she was not the standard trope for these jealous old friend types who tend to turn out to have changed a lot and become a villain from jealousy. That's where it looks like it's going initially but she turns out to be more heroic then expected. The Laser Puppies are just adorable. Their are other characters but these are most of them, ones that appear in multiple episodes.
In general, the characters are fun to watch with clearly defined and entertaining personalities but tend to be overtly simple, doing pretty much exactly what you'd expect.
A lot of the episodes in Star are (or at least seem to be so far) one-shot filler. I'll be honest, I'm a pretty big opponent to filler, preferring overarching plots.
In terms of individual episode plots, they vary greatly like most shows of this type too. The lowest rating I'd give any of the episodes is a 2 (my least favorite episode so far is "Lobster Claws" which I felt was confusing, had unclear motivations for the characters, and didn't have a while lot of laughs or interest) and the highest is a 5 (Freeze Day which is an absolutely beautiful piece of art which shows the relevance of Star and people like her, explains her virtue in a way that is both meaningful and understandable, has again beautiful commentary on the nature of time and perception and repetition and featured a binding of the universal and the personal which is truly the moments I watch Magical Girl shows for). If you were to watch just one episode of the show I would definitely recommend Freeze Day, it doesn't even need the preceding episodes because it shows the characters so strongly.
It's hard to talk really about overall when the plots are of very different natures, which is another reason I dislike filler.
3/5 (it's pretty close to 4/5 though)
Star versus FOE has a hypergirly aesthetic.....there are two female aesthetics imo, hyperfeminine which is more exaggerated, extroverted, youngish and involve classical female symbols, examples in Star include Laser Puppies, Star's Unicorn Obsession, The Rainbow-Based attacks etc. Their is also the more subtle feminine aesthetic which tend to involve long panning shots of peaceful areas, costume design, classical archetypes that such as the moon, water, mother earth and nature, etc. Star has a little of that too (like the panning shot when it shows Star's dress in Blood Moon Ball) but for the most part it's more of the former due to the show's energetic nature. Neither is better or worse mind you, it depends on execution.
I'm happy to say Star pulls of the aesthetic well imo. They symbols are used often enough to be motifs but not so often that they become overtly cheesy or expected. When I say that Magical Girls involve the feminization of power, and the users of feminine power, Star really does emphasize that with attacks and power specifically using female imagery Star's various outfits are all very cute and emphasize her open, adventurous, optimistic and bubbly personality. She also wears devil horns which I suppose is to emphasize her mischievous and chaotic (though benevolent) nature.
The worlds Star visits are also very well realized, Everywhere from Olga's Reformatory School for Wayward Princesses (Princess Jail) to The Plane of Time, to Marco's house is fleshed out and feels like a real tangible environment, even though they are fantastical and really quite imaginative, for the most part.
If I have any real complaints it's on the lack of visual cohesiveness. It's not a huge problem but a lot of the character designs, location designs, equipment, powers and so forth feel like they were designed in isolation. If you look at Ludo and his henchmen, they all look really different even though they (or at least some of them) are from the same world? Their is a sort of chaos in the design of everything from city design to Character outfits, with mismatched colors and sizes (thought Star's outfit is still adorable). Thematically this might be to further the feel of Positive Chaos that Star represents but it reduces a bit the level of iconic-ness that can be had. Although I suppose points for originally that they didn't take the easy route of just copying designs like is common in Japanese Magical Girl Franchises.
Also Musical Aesthetic quickly. The Opening theme I go on a bit of rollercoaster from "THIS IS FUN!" to "OMG THIS IS GETTING REALLY LOUD AND SUGARY FOR ME". It varies I guess how much I like the OP, though the "GOOD TIME" part and the story behind that remains crazy cool to me. The Ending theme has remained consistenly good, being much calmed which still a good reflection of Star's character (Particularly "I think that strangers are just friends you haven't met.")
Star vs FOE is a comedy, in what we Japanese might call a "Bubblegum Pop Comedy", as in a high-energy sugar-ball kind of comedy. So for the mood category I have to judge how good a comedy it is. And it is for the most part really funny. I will give it that. It's not the funniest thing I've ever seen but it's got good quotable lines. It's very good at keeping it's style of High-Energy going without ever becoming tiring which is a real threat when dealing with so much excitement.
It hasn't tried to be really serious much, but it has been pretty effective particularly in the last episode with 1 very badass moment ("No."), 1 very saddening moment, and 1 very heartwarming moment. Hopefully it can keep up the ability to sparingly use it's seriousness for real dramatic weight.
Genre (Magical Girl):
Star vs FOE is a Magical Girl show, a genre I have personal great investment in. You might think I'm biased towards loving with Magical Girls in it, or you might think as a true connoisseur I'm more picky about my Magical Girl entertainment. The truth is kind of mixture, I will be forgiving of faults if it's in the package I love, but I will always want it to be better, to push the genre to new heights. So how does it do as a Magical Girl show?
Star vs FOE is at the start of it a TEXTBOOK case of Cute Witch subgenre which is a tried and true formula (first Magical Girl Anime ever was Sally the Witch and was one of these) with the only real difference being that she got into real fights to save the world with bad guys and stuff like a Magical Girl Warrior would. But their seems to be more going. This time it doesn't seem their is a "good" and "bad" dimension as you usually see in Magical Girl Shows but instead a vast multitude of dimensions, and the villains actually come from Star's dimension, having been the original inhabitants before being pushed out. This is a very interesting idea but not much has been done with it. I'm not even sure the monsters realize that Mewni is their home dimension.
Beyond that it does a lot of the usual Magical Girl stuff (including formal dance with mysterious masked boy that makes your heart swoon and your eyes glitter <3) and it does them well. It's femininity is more in your face then normal which is enjoyable so long as it's not overdone. Star fits the mold of Magical Girl Protagonist well with her primary virtue signaling her role in changing the world (pretty much vital to an MG series), The Wand serves as a fine magical macguffin to fight over (and their always is one), etc.
Star does have some problems but a lot of it is things that are emblematic of the Magical Girl Genre. Magic and Powers not being very well explained allowing for whatever the plot needs, villains that don't act as real threats, protagonist-centered morality, etc. but as a Magical Girl show itself it shows the strengths of the genre more often then the weaknesses.
Overall I'd probably give Star vs the Forces of Evil a 4/5