Well, I'm not much into D&D or D20 systems (I do like the Eberron setting, though) and I don't fancy pre-made adventures with every detail prepared and every room having its small map. Improvisation and rich storytelling are GM's best friends, not miniatures being moved on a hex-grid (although it could be fun sometimes). But I'm still a bit uneasy with the declaration and compelling others' aspects system. Up to this day I was used to having the storyline in my hands and as a player letting it in the hands of the GM. This proactive system is ... interesting and definitely worth trying. I'm just not 100 % sure it will suit me and my players. Which is of course a matter of habit and taste.
On a different note (I don't want to start a separate thread for every question I'll ask): What is your experience with the game-time and real-time ratio? I mean does the game-time in your games tend to flow slower or faster than real-time? For example, if I start my campaign in the autumn 2012 I don't want to have the year 2015 in my game after six months of gaming real-time. And vice versa. This is no problem with most settings but with a contemporary campaign it might be. Thanks.
Depends on how you run your game. Do you do a bunch of time skips? Do you start a session by saying, it's now 3 months since you killed that Black Court Vampire? When traveling for days, do players just arrive or do you Role Play it out?
As to your issue with aspects, this is both a narrative focus game, which you seem to have some experience with, and a shared control game. It may seem odd and different, but it's the same thing as you've been doing before. Instead of having to improvise cause your players decide to go into the forest instead of the castle, you now have to improvise because your player has declared that he knows you're main NPC from highschool, or that you're dark mysterious sewer happens to have a recently installed light system. If you're into podcasts,
here's an episode that deals with the general idea of letting players define the world and a more traditional GM objecting to it, so basically this conversation. It's something the majority of the people on the cast had been doing since well before aspects or Fate.
My real life game has a bunch of traditional players who are just starting understand the shared component of the fate system. For the first few months, Aspects, Fate Points, and declarations were actually minor things, really only being used in the same way Savage world uses bennies, or D&D uses the GM's best friend +/- 2. I think you'll group will use them more like that, and you'll find it's not much different from the games you're used to. If you really want to start playing with shared narrative control though, get Fiasco, A Gmless game with no form of conflict resolution. Also worth checking out are Dread, Inspectres, and Wushu, which all have GM's but different models of control and conflict resolution.