And I'm behind again!
My #24 is Demon's Souls
My #23 is Resident Evil 4
My #22 is Gears of War 3
My #21 is Dragon Age: Origins
Now here's the clue for the #20:
"This is the sequel to game based on an already established universe born from movies. This sequel in particular had to had more than the 40% of its content cut to meet the deadline, and the developer wasn't the same one as the first entry."
20. Star Wars: Knights of the old republic 2