The past couple of days, I've been spending a couple hours a night watching tutorials and painting environments.
(EDIT) Dang. I forgot to make the images 800 px wide when saving for web. WARNING: You may have to CTRL+- to make the images smaller.
Obviously these are unfinished pieces, but the composition is decent. My only suggestion would be to work on defining your foreground, middle ground, and background better. Try using a fuller range of values in your concepts. Other than that, its pretty sweet! I can definitely see you improving fast.
Make yourself a perspective grid and be sure to not get bound by it than spend 2 or 3 more hours on you works. If you're starting it's not a big deal if you need 8 hours to bring your drawing to an acceptable state (i don't believe in finished-unfinished stuff cause as much as i know you can keep adding details for years...).
I hate to say this to you but right now you're somewhere near at a very bad sketching (very bad cause perspective is always off, you must work on fundamentals before anything else).