One of the better animes I've ever seen. Top notch stuff. Everything about this anime was just really well done. I loved the characters, (even if most of them were portrayed differently from the manga). There was action, there was comedy, and there was sorrow. Everything really was put together beautifully.
Story- Very interesting story. I didn't read the manga so even when I started watching it, it wasn't outrageously hard to understand. I actually didn't know this was a prequel till later, so that's a good sign at how easy the story was to follow.What I have to say about it thought was about how misleading the first episode was. Not gonna spoil too much, but there's a hot chick on a motorcycle wearing a tight orange jump suit. Mmmmm sexy.
Art- Art was A+ in my book. I've never been big on the realistic look. I've always enjoyed the slightly cartooney and colorful art style, and Ga-Rei -Zero- had that. The fight scenes were great. They were easy to follow, and featured some really bad ass moves. Definitely the type of shounen somebody might like if they enjoyed giant monsters fighting each other and ridiculous fight scenes pulled off by little girls. Gotta see it to believe it, but once again, A+ grade stuff.
Sound- Sound was good. Loved the voice actors, they worked really well to pull off the characters emotions. Sound track fitted the situations nicely and I liked it alot. I'm never to picky with sound, but Ga-Rei -Zero- was good.
Characters- Awesome character development. I really felt for them in their times of peril, anger, and joy. They each fitted into the story nicely, and all played their parts. They had some love going on in their (which I adored cause pairings are what make animes worth watching when people aren't hacking each others heads off), and some slight yuri if you could call it that.
Enjoyment- Enjoyed this to put it simply. It was fun to watch, I rarely got bored (it had it's slow moments) but they were able to pull through with some gut busting fights. Still nice for those who enjoy the mystery and suspension of wondering what's gonna happen next. It had it's drama, and all in all, it was a really well rounded anime that I think a lot of people could easily enjoy, even if they don't like the whole shounen idea.
Overall- Definitely one of the best animes I've ever seen, like I've said before. It had everything I liked. A little love, drama, action, fanservice. It was awesome. I recommend it for anyone to watch.