I'd love a sequel to Jade Empire and Kotor, but since those two have already been said I'll try a few ones that I haven't seen said:
Kingdoms of Amalur: I know it didn't get the greatest of reviews but it was still a damn fun game with interesting story mechanics and a great world to explore.
Toonstruck: That was a beautiful game that I believe was never finished due to a perceived lack of interest, such a shame too since the original was so good.
Theme Hospital: If this game wasn't part of your childhood then you should probably pick it up on a site like gog. It was an amazing premise that unfortunately never got a modern re-release.
Kingdoms of Amalur: I know it didn't get the greatest of reviews but it was still a damn fun game with interesting story mechanics and a great world to explore.
Toonstruck: That was a beautiful game that I believe was never finished due to a perceived lack of interest, such a shame too since the original was so good.
Theme Hospital: If this game wasn't part of your childhood then you should probably pick it up on a site like gog. It was an amazing premise that unfortunately never got a modern re-release.