1st half of the anime makes some improvements on the manga, like the kid who sits on a pillow's story. I cared for him in the anime and not in the manga mainly because they had more time time to develop his story. 2nd half is a little of lol Gonzo going on. It's not bad, but when you compare it to the manga it's crap.
It also makes a lot of tiny changes, for censorship reasons and what have you you. But ti also makes a lot of big changes, like the changes to fat kid's story. The two page spread where he meets the other pilot is one of the most moving panel I've ever seen, but the anime changes his whole story and fucks it up.
1st half of anime is better than the 2nd, manga's betetr overall.