Pirates was one of the games I was going to mention but I forgot. I think it would definately be huge if a decent sequel was made. There have been a couple of pirate games like Cutthroat but IMO they sucked. There is a Pirates Online but I don't know if its got anything like the traditional Pirates.
@Shatterhand and Drake1009
There have been other games in the X-Com series, but none of them were the same as the original. The second was underwater which I didn't like and it was also alot harder, but admittibly it made some improvemments like to the research system. Apocalypse followed a different concept I think, you had to stop the Aliens infiltrating governments and fought in office buildings and tower blocks. The other games in the X-Com series are IMO not even worth counting, although maybe the email game is okay.
The other problem is most of X-Coms sequels are old too, or at least TFTD and Apoc are. I want a nice, new UFO that is like the original although it might be cool to have UFO and TFTD rollede into one. With todays technology they could make the game more vast and varied, when it comes to the tactical combat. Rather than interceptor being a seperate game they could just incorporate a simple flight combat sim into the game, which should be optional. Now that I think about it if they combined UFO, Terror, Apoc and Interceptor it might make a really good game.