First I got there was on a grey and windy weekday. First thing I noticed was a friggin' Blenheim flying overhead! How many are airworthy, I guess only one left. And my eyes really started to pop when we entered the restauration hangars.
Second time I went there on a rainy Sunday, the BBMF was stationed there for the weekend, for an airshow at RAF Cosford (? can't remember exactly).
We were in a hangar until we heard the roar of half a dozen Merlins being fired op. We ran outside and saw the Lanc take off, followed by a Hurri and two Spits. Joy.
Duxford aside, Britain is full of great aviation museums. A few years back I was testing automotive GPS systems in Engeland and me and my driver were/are great aviation enthousiasts. And it seemed that every damn day we stumbled across some old WWII airfield with a tiny museum next to it, with an elderly lady selling tickets. The stuff we've came across is amazing. We usually ran in at 4 o' clock, the old lady would invariably say 'we close at five dear' and we would run around gasping with cameras clicking like mad. Great days. Should go back some day and do a tour with my new photo gear.