Hey, looks good... the normal map seems to have worked out pretty well. And the sculpt is looking good. But i agree about the underside of the critter not working so well. Insects/arachnids have an exoskeleton, so you would not see any muscles at all. But rather hardened plate, like armor. As in the image you posted. But as this is a cross between a humanoid critter and insect type critter you should be able to get away with some human elements. But, I think this takes from the believability..... even though a critter this is pretty unbelievable as is
The only other issue you might have (on a design basis) is the brain. The rest of his body seems (somewhat) armored, however, his brain, probably his most vital organ is exposed.
Maybe if you brought up the head, to more of a point, with a big armored head-cap/bone configuration. This will help to bring the design together.
But.... that's probably preference... you know what you want, and what you like.
Nice work!
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