Well, his writing of characters has been simplistic from day one but they are characterized well enough to be distinct and memorable.
He never explored many interesting possibilities (um, what about that half danger beast dude? How the heck is that actually possible again?), like I've mentioned several times, most notably Syura's plot that got wrapped up way too quick and (mostly) forgotten. On the other hand, the main storyline is filled with epic action.
Like I said before, it is written similarly to a video game. Yeah, it doesn't work as well as it could have; but unlike some of you, I've never felt the vibe of this manga changing. Maybe it's due to the fact that I've read 50 chapters of it at once - it has a pretty solid overall feel for me.
OT: I kind of wish Esdeath's obsession with Tats was portrayed as creepy from the beginning (like in this chapter where she doesn't mind doing it to his corpse). This way less people would see it as some "redeeming quality", believe that she can change etc.