Worth noting: Marvel vs. Capcom 2 is coming down off PlayStation Network and Xbox Live soon due to licensing issues. No word on the iOS version, but it seems reasonable that it might not be far behind. I would say if you're interested in MVC 2, now would be the time.
I got mvc 2 running on my iPhone through gridlee a month ago. Very sluggish.. but it was actually running.. which was cool.
