I didn't have time to see it in theaters, but I just finished watching DVD rip floating around online (well it has Korean subs over it, but the audio's still in Japanese at least, and I'm studying Korean so it's kind of win win) and I have to say... AMAZING. Mamoru Hosoda does it AGAIN; I didn't think he'd be able to top Toki o Kakeru Shoujo, but Summer Wars blew my mind. I recommend this movie definitely, yes it's anime. I saw an English subbed version while I was searching, so you can easily give it a quick Google. I didn't check the subs to see if the quality was good or not, but I wouldn't set my expectations too high since the only version floating around was that Korean subbed version I mentioned, so they most likely placed English subs over the Korean subs (it's most likely a mess). BUT I still think you guys should watch just because it's THAT good. Everyone I know who's taken my recommendations into consideration, well you know how accurate my quality sensor for anime is. >W< Any who, just wanted to give notice to you guys, whether you choose to watch it or not is up to you of course.

tl;dr:
Watch Summer Wars.