Yes, they definitely fixed a lot of problems. It's more balanced this time around. The AI in 3 would either flat out cheat or cross into your territory repeatedly and that really bugged me. Plus, it seemed like the AI would go to war with you over ANYTHING, and that was really frustrating.
Just what my wife doesn't want to hear. Anytime I bring up anything with the PC, she knows it's going to be pricey. I'm probably going to putter along with my 512 RAM and 9800 PRO until my birthday early next year and then I'll just build or buy a new desktop. Besides, I still have valks to buy!