It's not going to suck, if anything in the same way the first Transformers movie doesn't suck. Simply having live-action Transformers was such a mind-blowing experience you just didn't care about the acting or the story.
Simply doing TRON with those visuals and that cast will, in my mind, guarantee I will love it and will not notice bad story or acting.
But c'mon, you really think Jeff Bridges, Bruce Boxleitner and Steven Listberger would be involved if yr had any chance of sucking?
I want TRON New Rocks BTW ;-)