For the purpose of simplicity, feel free to conflate "worst" and "most disappointing," since we usually have a hard time keeping any distinction between the two in threaks like these. I'll start off with two sequels I've recently gotten around to playing (and loathing): - Civ 5: a pale immitation of Civs 3 and 4, dumbed down considerably. - Dragon Age 2: total omfg horseshit. Also dumbed down. Horrendous letdown after the original, which was excellent if not necessarily groundbreaking. I couldn't force myself to invest more than a few hours in this game before throwing in the towel. I can't even bring myself to finish it out of obligation, which is what I usually do with bad RPG sequels in franchises I otherwise enjoy.