just had to give impressions fo this to a friend and I'll see what I can remember of what I said...
first, the beginning is ass, skip the first episode. Even after skipping the first episode, I thought the first handulf of episodes, except for the 2nd, were very very dull and stupid. Eventually though, it became extremely interesting up to an incredibly awesome paek somewhere around ep 18 or so (I could be waaaay off on that). But by then the series has begun its violent skew into a seemingly completely irrelevant tangent that continues till the end of the series. This tangent, while not bad in and off itself, I felt was no where near as interesting as what was happeneing before it.
The ending was... acceptable. The idea was there, but I didn't like the way it was presented so much.
people always bring up bebop and berserk in comparisons, and while I see where they are coming from, I think its a bad way to describe the anime to someone that has never seen it before. I see the similarities but, they are similar in ways that just because one likes berserk or bebop means nothing as to whether or not they will like gungrave.
overall, thumbs up.