Agree Pirate Falls, Dragon Coaster in the castle, Viking splash.
In hindsight maybe I should have got Qbot, but I feel it's all so expensive anyway.
Take packed lunch (and tea) and eat down at the lighthouse show, always fun.
Get there before 10am definitely, run down and start at bottom.
Kids like the mini world, all the countries in minature.
Also on the big signs at the top that say queue times, I wouldn't believe them either, it said the roller coaster was closed, but we could see people on it, so ran over, and still had to queue 40 mins!
Take Top Trumps or something to play with in the queue so they kids don't notice the wait too much. Sweets useful at this point too. Go for a wee before joining the queue, so many poor parents were struggling to get out of the queue and go back to take a small child to the loo.
If queues busy the shows are good, and lots of places to go inside and build lego.
Take cagoul or waterproof cape (they do have them for sale there on the stalls).