I went last week and would recommend it for a fun 30 mins or so in the exhibition (it's not huge but then again it's only 3 quid).
The flight simulator (45 pounds for 30 mins) was my highlight. You need to book in advance. I also noticed at the ticket desk that they offer an early bird price of 35 pounds for 30 mins from 8am - 10am.
The simulators aren't as realistic as you would get in a full flight sim or even some of the fixed 737 simulators they have in places like Westfield London. However, it's good fun for a little bit of a spin.
You get 30 mins and you can swap around with your friends if you wish. The guy running the show is pretty friendly. There are only two airports, London (LHR) and Dubai. I just did the advanced landings. The stormy weather didn't really seem to work (I was looking for the hardest setting). It may have been simplified a lot for novices as I landed perfectly (but I play a lot of flight sim games) while my friend who doesn't struggled to get off the ground. I guess they have to find a middle ground somewhere.
All in all I'd say a fun thing to do if you're passing the O2 / North Greenwich.
We went on a Sunday morning at 11.30am and we more or less had the place to ourselves.