So I actually finished this series about two weeks ago now, but I find I need to wait to give properly objective reviews, otherwise all I'll come up with is keysmash and fangirling. So, now that I've let it sit a bit, let's get started, shall we?
Story: The story itself isn't anything new, honestly, as it has bad guys who want to destroy/take over the world, and a group of people who want to stop them. In that sense, Star Driver's basic plot is actually quite predictable, good guys always win, etc. However, the way in which Star Driver handles these problems and such is somewhat unique, introducing mechanics and limitations on both heroes and villains which can only be overcome by accomplishing certain things. So, while the plot may not be the most original, Star Driver is still a fun, fresh take on it, which keeps it interesting. Also, the pacing was pretty good - it falls into the same trap of leaving a bit too much to the very end of the series, but it certainly isn't as bad as some other series, and it isn't anything most people couldn't handle. It certainly has it's moments of pure crackishness, as it spends the first few episodes not really taking itself too seriously, but once it settles down, it's definitely got a lot of darker moments, too. Unfortunately the fight scenes tend to be kind of copy/paste, which loses points for me. But at the same time, magical boys. And girls calling themselves magical boys. This series made me laugh, but also made me emotional.
Animation: Absolutely beautiful! Lots of colours, lots of details, visually stunning. The fight scenes are absolute works of art, even if they're repetitive. The colours make sense with the atmospheres, so dark scenes have dark colours and light-hearted scenes have bright. Of course it has a somewhat distinctive style, so if that's not your thing, I guess you wouldn't like it that much, but if you do/can work around that, it's definitely worth sticking around. The opening and ending themes are cute, too! The animation is smooth, and when I said lots of attention to details, I meant it. Even the backgrounds aren't just static, at least most of the time. Except when they're supposed to be (during Zero Time, but I won't get into that).
Sound: Both sets of intros/endings are quite fitting for a somewhat light hearted mecha anime. The voice acting is great - every character sounds distinctive, and their personalities really shine through. Really top quality. Then there are the insert songs, which I absolutely adore. Haruka Tomatsu ("Sakana-chan")'s song, Monochrome, is probably my favorite of the four, but all of them are quite good! (Of course, that's a matter of personal preference, as music always is.)
Characters: Okay, here we go, here's where I get absolutely rambly. Like, multiple paragraphs rambly. Star Driver does characters so amazingly, it's... Kind of incredible for an anime of this length, actually. The easiest way to put this would be "You get a backstory! And YOU get a backstory! EVERYBODY GETS A BACKSTORY!" because it's true. Damn near every character gets at least half an episode dedicated to them: why they're on the side they're on, what their beliefs are, who they like/dislike, etc. It's absolutely amazing. This comes at the price of some plot pacing, unfortunately, but personally I didn't find the plot so rushed that this is a bad thing. But since nearly every character gets a backstory (which is what I was saying was rare for an anime this length - usually character development gets shoved aside, I find), they all seem much more relatable, which for me makes it so that there are actually very few characters I dislike. Even characters you start off disliking may grow on you once you get to learn why they are the way they are - of course, that's not a guarantee, and could just as easily go the other way (as happened to me with one character), but still, at least you can have solid reasons for liking/disliking almost any character. Again, not that that's mandatory, just that we can genuinely get to know each character and decide on your own terms whether you like them or not, it isn't just based on a five minute snippit of them. I find it quite refreshing, honestly. It's one of the things that makes this anime so amazing for me, hence the perfect 10/10.
Relationships gets it's own paragraph. So, if you don't want rambly shippy talk, skip this paragraph! Also this paragraph is... Slightly spoilery? Not really plot-wise though, just character-wise. I'll start off by saying Star Driver does something a lot of other series won't/don't do: threesomes. (I mean, there's no sex scenes or anything! Just keep reading.) Wako, the main girl, is in love with both Takuto and Sugata... And never has to choose between them. Never. Even in the last episode, she still has both of them: and they're both okay with that. Well, I mean, mostly, anyway. Both Sugata and Takuto wonder what will happen to them if Wako chooses the other, but for example, Sugata (who is actually engaged to Wako, and has been since before Takuto arrived on the island) asks Wako on a date, and then says that since Wako went on a date with him in the morning, she should spend the afternoon with Takuto. On Wako's birthday, Takuto gives her something precious of his, and when Sugata isn't sure how he's supposed to even match that, Takuto gives Wako something precious of Sugata's. Even as they're supposed to be competing for Wako's affections, they both basically refuse to. Of course, some people (myself included!) see Takuto and Sugata as actually interested in each other as well, but if that's not your cup of tea, that's fine too! (Except that Wako wants to see them make out, too. And more. And basically tells them as much. ["How long are you two gonna make out in there?!"]) And that's just the main trio! There's another important threesome, too, but basically everything about it is spoilers, so I won't talk about that one. Actually, there are really a number of possible threesomes/moresomes(!!), and practally everyone in the cast is arguably bisexual, or at least bi-curious. There's also a somewhat-canon set of lesbians whose stories don't revolve around the fact that they're lesbians; in fact it's never explicitly mentioned, but it's preeeeeeeetty heavily implied, hence me saying somewhat-canon. Also a lot of the cast wants Sugata or Takuto or both. Basically, if you want to ship something, go ahead. This series gives you a lot of room, and a lot of characterization and interaction to back it up with!
In conclusion, is this one of my top five favourite animes? It... Might very well be, actually. Of course I'm not guaranteeing that you'll love it as much as I do, but I think if what I've said so far seems at least marginally interesting, give it a shot! And if you're worried about/turned off by the mecha aspect, keep in mind that I personally don't typically like mecha anime either. The visuals are amazing, the story is told in a way that allows you to get to know almost all the characters individually, and in their "teams" when applicable. Tons of shipping options if you're into that. Just... So many things packed in without coming off as overwhelming. If you're debating, or even just slightly interested, definitely give it a watch!