His right armpit area is incorrect. The pectoral muscle flows right into the deltoid muslce, and there no extra bit of intersecting form at the armpit.
http://www.muscleprodigy.com/content/articles/home/sculpting-a-masterpiece-biceps-712.jpg
http://www.123rf.com/photo_4233974_strong-man-measuring-his-bicep-muscle-isolated-over-a-black-background.html
http://image1.masterfile.com/em_w/03/38/24/695-03382419fw.jpg
The left hip area looks odd too, with the orientation of the thigh totally unreadable, or how it connects with the hip.
I would suggest you take photo references of someone in this pose (either yourself with tripod/mirror/timer, or a friend/family). If possible, without shirt and with similar pants as what the character wears. Also use household lamps to get the lighting the way you’d want it to look in the painting. Once you have a reliable reference, you can then exaggerate it to suit the unique proportions you want (can even use the Liquify tool in Photoshop), and you’d get much closer in terms of anatomy. Of course, the more visible the muscles are in the reference, the less you have to guess or piece together anatomy references from elsewhere, so if the model has a physique similar to the Lifestealer, that would be ideal.
If this is meant to be a full painting, you need to start working out the composition for the entire painting, not just the figure in isolation. The figure is merely your main focal point, but there must be supporting elements and counterbalances to the focal point. (Unless you want a painted figure on a blank background, which is not generally a good idea unless for a specific type of usage.)