Got in the queue around half 8 on the Sunday.
Think we were supposed to go in at 9 but after a bit of delay they started letting people in around 9:20.
Short story - there were various performances & interactive things.
Longer, spoilery version:
There were people dressed as various Alice In Wonderland characters outside. Group of people had some teacups and Alice let them skip the queue.
Got to the front of the queue and had to crawl through the Mad Hatter's legs to get into the tree. Had loads of cool decorations inside, crawled through some more legs then someone gave me a flying saucer sweet.
Then Tweedle-Dee & Tweedle-Dum were by two doors and I had to pick one. My partner & I also had propeller hats which they loved. I went through the 'Dum!' door which let to a tunnel I had to crouch-walk through & out of a large vagina into a larger Wonderland themed area.
This area had a bar which only sold cocktails at a tenner each (only had the 1). There was a stage with various performers, I remember a drag performer & someone called LYNKS. They also brought members of the audience on stage for various games like a dating show.
There was also a club bit with DJs & sometimes Alice & some mushrooms would dance on it.
The Queen Of Hearts also came out and played hedgehog croquet with Alice.
Had so much fun there we stayed until 3am and missed all the Sunday headliners. Apparently the likes of Louis Theroux, Noel Gallagher & Rita Ora were about but I didn't see them.
Would definitely recommend going in at least once but definitely best to get in the queue pre-9 to really experience everything.