I was very LTTP, just picked up Ultimate MvC3 last weekend for $14 on PSN. Holy shit it's terrible. I seriously don't understand how the company that made MvC2 could release something so utterly devoid of fun. If it wasn't for RE7 being so horrifyingly entertaining, especially in VR, Capcom would be dead to me.
I've been trying to go back to it also with the supposed leaks for MvCI... I'm sure we'll both be roasted for it, but I totally agree with you. The game just lacks that special something that I can't put my finger on to make it fun.
On the other hand, I greatly enjoyed TvC, which came out just a few years prior.