Time travel in fiction comes in two varieties. One is the sort of unexplained, mysterious force that you accept and don't question for the sake of entertainment, like in The Time Traveler's Wife or Back to the Future. The other is found in films like Primer and Timecrimes and is intricate and confusing, but if you pay attention you'll at least understand 25% of it -- you'll get the other 75% when you read the fan forums, unless you are smarter than me and are the one posting the explanations.
So far, we've only had the former type realized in games. Titles like Braid, Blinx, and TimeShift treat the premise of time travel like it's a VCR. You rewind, pause, and fast-forward time without ever having to deal with the consequences of alternate timelines or paradoxes.
Achron is a different kind of game that turns the time travel gimmick into a fully-realized concept that opens the doors to new strategic and narrative possibilities in the real-time strategy genre, though at a substantial cost to functionality and presentation.