Favorite Game of all time....Has to go to Final Fantasy VI.
Hands down the best Final Fantasy ever made, sorry to all the 7 fanboys and fangirls, it had no replay value. I played it, I beat it(seemed short) and I stashed it away with the rest of my games.

On my original cartridge of FFVI for the SNES I have maxed the game clock out on numerous saves. For the PS I maxed the game clock twice or so. And for the GBA I'm still playing it more and more. I lost count how many times I've beaten the game, its well over a dozen times. I'm gotten everything that there is to be earned in the original version. Now I'm working on the GBA version to see how they updated it and whats been added. Looking forward to the new dungeon that was added for end-game content.

In close second would be Guild Wars. I've never found a game that was playable like this one. I've logged well over 2600 hours in the game over a 2 year period and still havent everything I'm after. A great guild with fun people to game with always enhances the gameplay and on going evolving game play makes it ever changing. With a new expansion on the way this year and Guild Wars 2 Beta due in 08 I foresee a lot to come from ArenaNet for this game^^