The Cardiff Nationals of 2012 were - to my knowledge - the first to have Doctor Who as one of the categories for RPGs. Of course, when I found out about this, Doctor Who was my first choice as a category. Both games I played that weekend were great fun, but I especially liked the first one I was in, which utilised a 3d10 system which has been used in two or three different games published by Jackalpack Games. It wasn't so much the system itself that I loved (though the system was good as well) but the scenario, the pregens and the way that the Doctor was handled in play were really cool. I don't want to go into too much detail about the scenario itself - I might adapt it for my own purposes the next time I run DWAiTAS - but I'll tell you a bit about the pregens and the 'Doctor mechanic'.
First off, the TARDIS crew consisted of a teenage hacker who had fallen in with the Doctor, said teen hacker's mother (a lawyer) who joins them to keep her son out of mischief, a friendly cyberman, an anthropomorphic rabbit princess and...I can't actually remember if there was a fifth or sixth character, those are the ones that stuck in my mind. My favourite out of the pregens was the mother and son duo; I might be a bit prejudiced since I was playing the mother, but I just loved the dynamic that added to the party. Also, as the mother I not only mothered my 'son' but the party as a whole...Doctor included. ("You may be a thousand-odd years old, but if you will behave like a child then by God that's how you'll be treated.")
Speaking of the Doctor...deciding who gets to play the Doctor/Time Lord character in a Doctor Who game is always one of the sticky points, since it's such a powerful role. I avoided it in my own campaign by having the whole campaign revolve around his disappearance, but this game took a novel approach to the issue. No one person played the Doctor. For the most part he was a passive NPC, mostly contributing exposition; but if we wanted him to actually do something more active, then we could temporarily take control of him as a player character.
To prevent people from hogging the spotlight as the Doctor, the GM gave everyone countdown clocks which we could use to clock in and out of 'Doctor time'. Everybody had five minutes of 'Doctor time' at the start of play, and could earn more as rewards for good roleplay as their own characters. Once their 'Doctor time' was finished, they couldn't play the Doctor anymore. As a result, when people clocked in as the Doctor, because of the time limit they played the role with the frantic energy that's typical of the character when he's in action. Also, if the other players were anything like me, they had thought through how they were going to use their 'Doctor time' beforehand and so they played with confidence reflecting the Doctor's certainty that he (mostly) knows what he's doing.
Okay, so it probably wouldn't work for longer-term play, but as a gimmick for a one-shot scenario it worked beautifully and I would use it myself if I had the cash to burn on buying a whole player group's worth of countdown timers. Sure, I could just use an app on my mobile to keep track of everybody's countdowns, but that takes away the tactile aspect of 'tapping in' to announce that you're taking over as the Doctor for a spell. In any case, it's probably the best game I've played at the Nationals to date.