It's been three or four years since I really played it all that much; it's a bit hard to remember. Difficulty and match length are the two that really stuck out - it was either way too easy to win or impossible to win, and either way matches were generally over in about three minutes each.
It also gets pretty dull after a while, just match after match. Universe seems like it's improved a lot in that regard. The lack of creation suite really bothered me last year, and I think they removed a lot of the ability to alter rules and things as well. I loathe escape-only cage matches, and I used to set all my cage matches to pin/submit only. My triple-threats were always elimination, etc. I could put time limits on, and it had the 'normal/epic' setting that meant some matches actually approached that limit.
I also had Universe set up with a custom ROH show in that tiny little custom arena, with the 2006-era ROH ring and custom ROH championships, none of which was doable in 2k15. Still can't really be done all that well with custom music still not a feature. I even had it modded to have custom titantrons. TBH that and the Action Replay era are the two I've used the most.