Way too many lines, and just plain messy in general. Try to make clean lineart, or at least practice making clean lines. That way it not only looks decent, but you learn the hand-eye-coordination you need to have when using a tablet. And then you can try making it purposely sketchy.
The lines look distracting and random, and I can still see the guidelines. Maybe if you did more careful hatching rather than the scribbly lines it would look a bit less chaotic. I assume you're going for a sketchy look, so you don't have to use super smooth lineart, but getting rid of the distracting lines would help focus it a bit more.
Please give me your honest opinion on how I can improve. So honest that I'll have no choice but to learn.