Stable servers. Seriously, that shit went down every other time I went to look for a match or a bit of created content.
Secondary to that, they need a massive update to the roster - stop recycling the same wrestlers and animations from the last ten years of Smackdown games already. I realize the CAW feature allows for the creation of practically anybody, but recyled animations and warmed-over taunts make it hard to really create unique feeling wrestlers. A more refined Universe mode is an absolute must, with the ability to make sure favorite wrestlers and/or feuds can be created and added with more regularity.
The CAW system is pretty okay, but a larger cap on the number of items that can be used or implemented would be a great thing. We probably won't see that until the next generation of consoles, but a fella can dream. Other than that, there are the usual suspects - make the crowd look better, less weird clipping, overhauled and simpler controls, and less goddamn HHH.
Yea, less Triple H.