I really cannot figure out if I like this manga or not. Most comments have already captured the pros and cons about it, so I'll just focus on my opinion.
Most important negative point: I think the design of the enemy makes it impossible for me to feel intimidated by them, therefore taking away a bit of the seriousness of the manga for me. I mean, seriously, if you did not ROFL at least once looking at those humanoid roaches, then something may be wrong with you (haha, kidding). It's like a crude parody of blackface.
The other issue is the character design. The storyline keeps jumping back and forth between different scenes, and I was often finding myself confused as to which character was which when they are not shown in their 'transformed' state.
In regards to the wanton death, in Gantz when important characters died, later on in the story there was at least a mention or revisiting of their existence, which helped cement the role they played, however short it was. In this manga, seemingly important characters die and then are quickly forgotten about. It makes me feel like the author is just having fun introducing character designs to showcase different mutation possibilities, and doesn't really care about the characters.
For me, honestly speaking, the one thing that keeps me reading is to see what other creature mutations he comes up with, and the creature intro panels. Other than that, not much really.