Hi, Justa! It's looking pretty good so far. The color looks really nice. Did you crop the actual painting or is that just a detail shot? I'd be interested in seeing the whole piece to do a better critique. I'm liking the shape of the gnarled tree and the bark textures.
From what you've shown, though, the main issue that jumps out at me is that there is still not enough skull. In reality, it may be that the features are too big and the eyes too high. I say that, because adding more skull may make the head look too big. The overall form of the head is also rather flat. The features look as if they've just been pasted on. You should try contructing it out of solids, so the eyes, nose etc. feel as if they sit in space. The hands are suffering from the same problem. They look better in your line drawing, but you're starting to lose some of their structure in the painting. Hope that helps in some way.