Mass Effect series. All the games pack hours upon hours of gameplay. I am currently 50 hours into Mass Effect 2, I am a bit close to the ending, but I want to complete side quests and get upgrades before completing the ending mission of the game (which is amazing). Mass Effect 3's ending was quite crap though, so that might be anti-climactic, but less so with some mods and the Extended Cut. Mass Effect 3's ending is final, though, but it does have a New Game + mode. I highly reccomend ME.