We were there on Tuesday and Wednesday and had a fantastic time.
Thanks to NoRoom we all wore our ski gear and were thankful for it. It is after all an outdoor attraction. There were lots of very cold looking people wearing coats and hats/ gloves so I think having warm legs and feet made a big difference. Lots of local school children arrived just before 4pm and they looked cold in their blazers and caps / shorts and long socks!
We queued minimally during both days - boat driving and the small dragon roller coaster were the longest queues at about 10 minutes each. We went straight into Atlantis every ride and the boys both enjoyed that. On day 2 both driving schools had extra cars on, and ds1 ended up going on 5 times!
The driving licences were pricey but we bought the 4 photos for £20 package so we got 2 driving licences and 2 other photos for that price. The photos can be bought at the ride, then the ticket presented at the Roaming Photos booth back at the entrance as you leave - very good so that they don't get squashed!
SQUID racers were enjoyed by both ds's. ds1 is only 2 cms under the height limit to ride alone, but there's no way he'd have managed to turn the wheel himself so it's best to ride with them until they're a fair bit bigger and stronger.
Parent swap worked really well whenever we needed it - just ask the ride attendants.
The Que-bot booths weren't even open as it was so quiet - I can see that they would be good on busy days if you can afford it (£15 per person per day for the most basic).
The 4D clutch Powers show in the Imagination Centre was excellent - both ds's are still raving about it!
Laser Raiders was enjoyed by all - the queues must get horrific judging by the amount of bollards that we walked through but we waited no more than 5 minutes and both ds's loved shooting their laser guns (I won though - obviously!).
We took drinks and snacks, but did eat in the pizza/pasta buffet which was good and very efficient and had tea in the Hilltop Cafe before leaving yesterday. They do mini pizza, jackets, fish fingers, panini s and lego shaped chips (v cool!). We also stopped in the coffee shop just to the right of the pizza place - upstairs is like a sauna and by far the warmest place that we found though it needed a good clean when we were there too. Lots of the food outlets are still closed this week - probably because it's still so quiet. The food and drink aren't cheap, but are no more expensive than any other tourist attraction in my opinion. As it was so cold, taking a picnic wasn't an option. There are places to eat picnics though.
Guest services is just on the right as you go in and if your dc are right on the limit of being able to ride then they can be measured there and give an official wristband saying that they are over 90cms to save hassle at each ride.
We parked in B2 and C1 which were both well positioned. I paid for parking both days (£3), but as we left quite late the bollards were open each time so I probably could have got away without paying!
We stayed in the Heathrow Premier Inn on Bath Road. It has a nice restaurant - children ate free for dinner and there is the usual good Premier Inn breakfast included in the price (we paid £130 for 1 adult and 2 dc for the hotel and 2 days in Legoland and got a £5 voucher for any purchase over £35). We had a room overlooking the airport which was fine on the whole but not for the 45 minutes or so late at night when they must have swapped runways and some massive planes were taking off - the sound proofing wasn't up to that!).
I hadn't factored that the M4 east would be so busy at about 6pm 
so by time we'd stopped to change ds's into pj's for the drive home, I had to peg it to get to the stretch around Bristol before it closed for the night due to the traffic management roadworks!
All in all we had 2 brilliant days and I would definitely do it again next time our school holidays are different to lots of others!