| Mmm... when you say replayability, do you mean your desire to drag them out or the likelihood of playing them? Or do you mean the number of times you can play the game without it getting boring?
Descent definitely gets my vote for replayability, especially combined with the Road to Legend expansion. Fantasy miniatures in a dungeon, with the expansion, you get a full campaign system and overland planning
Twilight Imperium is HUGE fun, but it takes a long time to play (3 - 4 hours minimum and more likely 4-6). Galactic conquest at its best. I hear Supernova is TI Lite - and heard very good things about it but not had a chance to try it yet. Tempted to pick up a copy myself since I have friends who have TI.
Arkham Horror is a Cthulhu (horror) game, so not sure it falls into Fantasy, but huge replayability. Again, lots of time. It's a Fantasy Flight Game.
I've heard lots of good things about Android too - I am tempted to grab that as well. It's a cyberpunk noir detective game - think Bladerunner for theme.
Moving closer to Euro's (so the theme is less apparent, but still sci-fi/fantasy themed).
Race for the Galaxy - card game about galactic conquest. Plays like San Juan but more complicated, huge replayability, but the game is a bit solitare like and while the theme is there, it's not as engrossing as any of the above.
Kingsburg - probably my favourite board fantasy game of last year. It's a politics / development game where players try to influence various characters on a board to help them build their city over 5 years. During winter of each year, you get attacked by a random monster. Again, theme is light, but fun. | 
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