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There were threads discussing what single player games should be made into MMOs. I figure i will try something new and have the question reversed.
Here is my list:
TOR - this is begging to be a single player game. I think it is a mistake not to just do an online KOTOR with better combat.
STO - some of the story missions can probably done very well as a SP game. Ground combat can be improved but space ship combat is FUN.
DDO - lots of the dungeon missions are similar enough to SP quest chains.
TSW - i have not played this game ... does the story mission work well in a SP or co-op mode?