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TF2: Reloaded
I honestly can't think of anything that would make the game better though, I mean...being able to create your own character I guess would be interesting or something like that, but it's still nothing that can't just be updated to TF2.
I'll put it this way, I can't really see anything that would be worth creating a new game over in the TF series, which is interesting to me considering I can't think of another game like that.