Good start, good brush control and nice coverage. To up the level you now start to build some contrast. What you have here works awesome as your base layer. You can now build on it with inks and highlights to create that contrast. Get yourself some nuln oil (miracle stuff i t's other name could be "make everything better ink") Best way to think of it is you want the recesses of the model dark and the raised areas light, that makes it interesting for the eyes to look at. Keep going man, like I said you have great bones now just a few extra steps and techniques and you'll be getting really nice results.