very graphic and violet
very bleak
goes to great lengths to make you despise the main character, his internal monologue establishes him as the most irredeemably terrible person in the world (which, actually, I found fascinating)
extremely well animated
the plot can move a little slow - for instance, the series deals with people sent on missions to kill what are presumably aliens, but the entire series consists of only 4 missions
as was already pointed out, the animated series ends abruptly and isn't very satisfying. Personally, I enjoyed it, but the abrupt ending irritated me and at some point I hope to read the manga where the story goes on for much much longer