Disregarding the fact that all RPGs are fantasy, I’ll assume we mean some form of "magic is real" type of fantasy genre. Mostly because we seem to be in "genre week" for RPGaDay, which would be great if I played more superhero RPGs. Ah, well.
If you read my blog, you already know that I’m a big huge nerd over Dungeon World, and I like the system a metric ton. But let’s step away from that and talk about a game I don’t often spotlight, even though I’ve been playing it for over a year now.
I was first introduced to 13th Age last year, shortly before Gen Con, and then played it in person at Gen Con. My online game group (the Moving Forward campaign, with Gwenn, Firiel, Tristram, and Ordune) had a break over the summer while we played Fate, and decided to play 13th Age when we returned to our campaign. Our GM spent a meticulous amount of time converting our characters from 4th edition to 13th Age PCs. It wasn’t easy– we lost levels and our powers changed quite a bit in the transition, but he did a good job of maintaining the "flavor" of who were were in the process.
I played a paladin in a one-shot game at the last Gen Con which went really well– converting Rose from 13th Age to D&D 5e was not hard, but playing her in the murderhobo world of Adventurers League was more difficult.
Right now, our weekly online game is playing 13th Age where we’ve changed the setting a lot. There are sentient dinosaur-like people, the world is quite a bit more "modern," and we’re some kind of investigators…. kinda. We’re still getting our feet under us in terms of the custom setting, I think– I actually believe our campaign might go better with a more freeform system, but this is what we’ve played for over a year, and the GM wanted to try using it for the setting he’d come up with.