Disappointing Sequals

I've got 2.

Knights of the Old Republic 2: -excellent game with a plot better than the first (actually, it does beat the first in most categories), but it's marred by an insane number of bugs and one of the most rushed endings I've seen.

Beyond Divinity - the original, Divine Divinity, was an awesome game for its time. Diablo's game mechanics combined with an open world and a lot of sidequesting. The sequel, however, rips everything good out of the first game and doesn't add much new. DB's extremely linear, has a horrible skills system (well, the system itself is good but you gain skill points at terribly slow pace) and some of the worst voice acting I've ever heard.