Those paintings are really nice! My only problem with them is that they look a bit too sterile, a little overpolished in a way, things look a bit flat and lifeless when you render them out this much. Would love to see more definition of form as Andrew said. I think adding some more texture and grit, and basically looking more at material properties would help these, and leaving some stuff looser would help too, as the focal points grab more attention then. This piece, by Maciej Kuciara shows what I mean. He lets the important parts get more of a surface treatment and a sharper rendering to really point out what the piece is about, even if it is a bit exaggerated. Everything else is really just a blur, but you still know what is happening.
Anyways, hope this helps a little, most of it certainly applies to my own stuff as well. Good luck getting client work, I've been thinking about trying to get some myself!
I agree with PieMonster and Andrew on the painting. Close up areas look great like the monsters face and muscles, but as a whole the values don't feel like they're working at the moment. I think higher contrast would help, but also bigger chunks of shadow/light to simplify some of the forms a little bit. I love the composition of this one and reckon it could be an awesome portfolio piece!!