(Only minor spoilers in this review)
Corpse party is... okay. It's not the best horror anime I've seen, but it's definetly not the worst either. Be warned, there are a lot of gore and violence, as well as some ecchi. It's interesting enough to watch (since it's only about 2 hours in total), but it could have been better. Have in mind that I have not played the game.
It's your typical horror story; some school kids perform a ritual and end up in a school that's haunted by the spirits of dead children and their victims. To escape, they have to solve the mystery of what really happened to the children, and set their spirits free.
The story works. It's unoriginal and predictable, but it works. However, you never know who will survive, or if anyone will survive, which I think is really good. The ending was also a surprise, as well as the characters actions.
The reason I give it a little above average on the story is because it had a few holes in it and they didn't show everything that happened (probably because the time wasn't enough). There were quite a few things left unexplained and some things the characters did were just plain stupid. I mean "this guy just told me there are ghosts here and the floor is filled with blood and corpses.. well, I'm gonna go find a toilet because I really need to pee right now, we can catch up later, bye!".
The character design and the animation was great. The gore was terrifying and well done, the lightning and shadows were spot on and the creepy stuff were indeed creepy. I liked the fact that the gore worked and was part of the story, and not just "there for show". Some facial expressions and minor things could improve, but overall the animation and art style was very good.
The sound helped create a creepy and mysterious atmosphere. The voices fit for each character (jap) and the soundtrack was good.
Oh damn.... this is where it really fell for me. It was almost like the creators though "hey, this guy/gal is just gonna die soon anyway, there's no need to give him/her a personality". They all had one of three personalities: 1. The stupid and scared one. 2. The stupid one that wants to save everyone and get them all out of there. 3. The stupid one that turned crazy. Did I mention they were all incredibly stupid?
There were however some characters you "kinda liked" and some you "kinda hated", but most of them were just there. There was no one I was particularly fond of and I couldn't care less about the ones who died.
As I said, it was okay. I recommend you give it a try if you like horror, blood and gore, but that's mainly because it's so short you won't lose much if you don't like it. However, if you are easily irritated when the characters make a stupid decision or hate plot holes, then this is not the anime for you. I have heard the game is much better, so maybe you should give that a try instead.