I have read a few of the Dresden Files books and enjoyed them so I thought the back ground would be pretty slick. I had never played the Fate system, and had only heard just a bit about it so I was looking forward to checking it out.
The first thing you notice about the Fate system is the dice. It doesn't use standard d6's.
Each die has 2 + signs, 2 - signs, and 2 blanks. When making an attack or skill roll you roll these four dice and add them to your appropriate stat (usually your stats will be between 0 and 5.) You then add one for every + and subtract one for every -. Easy as that. This gives you your result and tells you how well you accomplished your goal - 0 is a meager success while 8 is a legendary accomplishment.
The way the skills and combat work are all rolled into one. You don't have a separate combat system - it is all based off of your skill with your weapon (guns, melee weapons, claws, etc.). Weapons will have a set damage value, but this can be modified by how well you roll your attack and how well your opponent resists. I didn't play a combat heavy character so I don't have a real good idea how this works, but it was very smooth and lots of fun when we did enter combat.
The general way the game flows is you will arrive at a location and the scene will be set. The GM will tell you who is there and then you are off. You will usually have plenty of options for roleplay and interaction before you get to any combat (if there is any.) Movement is very abstract, you have range bands that are like this - if you are in the back room of a night club fighting a guy you are at range one. People in the main area of the club are at range 2, people in the parking lot are range three, across the street is range four, and on the roof of the opposite building is range five. You can move between ranges by using up your action so there is no need for miniatures or detailed maps.
My favorite part about this game was the character creation. Since it was a con style one -off the GM had pre made characters for us, but not all the info was filled in. Your main big skills were filled out (I was a mystic wannabe new-age folk lady so I had a high knowledge and perception) but your lower level ones are left blank for you to fill in while you play. Trying to chase down a guy in your car and you don't have the driving skill? Add it in. You now have moderate abilities at driving. Trying to break in somewhere and no one has the burglary skill? Have the shadiest member add it in and give it a shot. I really liked this approach and it is very close on how you do it for an ongoing campaign.
All in all we had an absolute blast with the system. There are tons of other really neat features that the system has and it is well worth looking into if you want a break from D&D or your current system.