It's ancient, but Day of the Tentacle is a pretty neat treatment of the subject.
That would be one hell of a game! Just update the graphics a bit, add in a more robust AI, and you've almost got a David Weber novel!I used to love Millennia:Altered Destinies - you wander back and forth in time in a space/time ship, making decisions for a few alien races to guide them to maturity so that they invent upgrades for your ship , ultimately to repel invaders from another galaxy. It's an old DOS game, but the most directly you-controlling-time-travel game I've ever seen.
http://en.wikipedia.org/wiki/Millennia:_Altered_Destinies
Tales of Phantasia, and... yeah.... Chrono Trigger.
Mission Critical was a fantastic adventure game. If you like hard sci-fi, I highly recommend finding an old copy and loading it up in Virtual PC.