Those are cool - I especially like the Alien Outpost one. That's one thing about art, as long as you are getting better you always look back and say, "I would do that differently if I was to do it now".
Personally, I am finding that while I try to use the software for a lot of stuff I don't always care for it except for coloring. There are a few really neat features it can do, mosaics and so on but it seems like when I draw it by hand and port something in, that hand drawn portion looks so much better than the rest. So, I'm still trying to find my balance between hand vs. computer produced effects. I have to think some of that is my not totally understanding what my software can do. I've been really thinking about getting a book and reading it.