Updated with some official notes via Capcom. Their list is not a complete or even comprehensive list of changes but it is official and does mention some things we didn't know about previously.

If they add split screen in a patch I'll buy the game

I played the game today and I noticed many changes. The versus ran really smoothly for me. My shots seemed to register better. I also noticed that the partner AI was better than it was before. They were actually helping me and didn't get stuck on stuff. Overall, I'm liking the patch and I hope they continue to fix the game.

I'm not enjoying the versus play atm for some reason... Runs a lot clunkier for me and I feel like a noob again, just can't perform as well for some reason, no matter what weapon I use.

Just to let people know, the grenade launchers still do instant kills