I love the first one, easily one of my favorite animated films of all time. Pixar are always pretty good, but other than Toy Story, their sequels have been kind of subpar (for their standard) and forced.
I'll co-sign all the above. The first one in fact is my fave animated movie of all time. The manifestation of baby Jack Jack's powers, he's the Superman (more powerful by himself than all other DC superheroes combined) of the crew. Could be a fun subplot if they choose to go the whole secret identity/we're just regular folk route.