Fable is definitely one of my favorite games. I love that my choices are able to influence the game. I've played the Witcher too and also really enjoyed it. I liked the fantasy setting. I've heard of Mass Effect, but I really prefer magic and swords over guns and what not. Anyone know any other games like this?
These are more classic games, but you might like Dark Cloud and Dark Cloud 2. Also, while not exactly the same milieu, you should play the first Digimon World. It's not very similar, but is every bit as fun.
Try to Dragon Age, it is a lot like fable and has the same feel for it. Can't recommend the new ones because I never got to play them so don't know how they would be.
I really like Dishonored. (In case anyone could tell from my avatar, lol) It's very much based on how you do things. If you go in guns blazing and what not, then the next time they will beef up security and make it harder to get in quietly. There is magic and such, but there are also guns.
Try the Witcher 3. It's like the Fable game that we all wanted, but never got. Huge world? Check. A multitude of monsters that you can kill to your heart's content? Check. Awesome questlines with morally grey conclusions? Check. An awesome combat that uses both fast swordplay and bursts of magic? Check. A game world that responds to almost every action you make in the game, both small and large? Checkity check! It even has a real-time beard growth like the first Fable game that had players age as they progress! Now how cool is that!
I'll have to agree with UnslassdKrosis Witcher 3 if fable was a first evolution it's intended last evolution would have been Witcher 3. Witcher 3 is everything that Fable isnt. You could try other sucessors like Skyrim and the newer Fallout series. They are good as well. Fallout New Vegas is what I'm referring to by the way.