In all honesty? Duke 5, by default. None of the other franchises recieve a single one of my fucks.
But if we're making up sequels, here are some I would get my jimminies rustled for:
Mirror's Edge 2
Shenmue 3
Capcom vs SNK 3 (using drawn sprites, not 3D)
Serious Sam 2 (by which I mean a retcon of the terrible 2005 game, and a proper sequel to SS: Second Encounter. Hell, a Third Encounter using the original engine would suit me fine.)
Splinter Cell 6