I honestly think that then entire online lobby seems like it was purposefully designed to be as annoying as possible. Chat rooms are as old as the internet, yet NRS (or GameSpy) completely ignored any sort of standard that has been built up.
I don't know how it is on the XBox but on the PS3 the text input buttons in the lobby are painfully different then those in the PS3 mailing system. I cant recall the exact inputs but I think Triangle is space in the PS3 mailing system and change character set in the MK lobby.
Messages can only be something like 32 characters long and there is no character counter (like twitter) or otherwise any indication of size. I keep trying to figure out why they didn't allow multi-lined messages or why they didn't get rid of the crap on the right side of the screen so that the messages could have more room but I cannot. If it was to save bandwidth on messages or to ensure that the chat wasn't filled with novel sized messages then they failed because they didn't put any sort of spam prevention...actually they facilitated spamming by allowing people to save messages.
Players cannot be filtered by availability. This means that if I want to find someone to fight, I need to wade through 50 people already playing a game.
Connections are always 4 green bars. I have never seen anyone on that list that wasn't green but I have had plenty of fights where it definitely shouldn't have been 4 green bars. Didn't we learn anything from vanilla street fighter 4?
Other than that?
The entire throw teching system in this game. Why isn't it just the throw button like it in Street Fighter? Why do I need to not only read a tick throw but then guess what direction they are throwing and then get no advantage for doing so beyond avoiding the throw?
Raiden's Teleport, its too fast and it places him close enough to me that he can throw, just compounding the rage for the above reason.
Any character that has a D+3/4 that has a hitbox that cannot be hit by a jump in.
Any move in the game which both comes out lightning fast AND has a quick recovery on block.