Online is pretty horrible so far, slow motion like has been said already. One thing that irks me is that you can't even enter kombat codes on UMK3 vs. screen. The 6 boxes show up, but you can't enter anything, like they just forgot about it or said screw it or something. It really doesn't seem like they gave much of a shit when they ported these games, so far.
Other than that, all I've noticed are some minor audio glitches with MK1. The uppercut sound bugs out, and the Goro's Lair music stops playing a few seconds into the third endurance match. Also the clapping in the Courtyard stage isn't the arcade sound, it's slightly different. Haven't noticed anything besides that so far. This is all nitpicky stuff, but with as old as these games are, they should have been able to do everything perfectly while blindfolded and writing code with a Speak & Spell.
Offline is arcade perfect, but I didn't buy this to play offline because I already have them all. Chances are online will be patched, but it's a major disappointment in the meantime.
Offline is pretty much arcade
