The only three franchies I'll miss by them that were developed: Blitz, Mortal Kombat and The Suffering.
Blitz 2 was supposed to be a lot of fun but was marked poorly and dropped to $40 pretty quickly. Blitz is not something that I need in my everyday life however, I was more of a 2k Football person.
Mortal Kombat is their best franchise and I'll sorely miss that. However, knowing sales and reputation of MK I severely doubt someone is going to leave MK in the dust. I hope Microsoft does some magic and gets Ed Boon and all the creators into MS studios so we can see MK exclusively on the 360 - that would be pretty big IMHO.
There was no info on a Suffering three which would be the only franchise I cared about deeply from them outside of Mortal Kombat.
It's just that simple.