Firstly, shame on the dodgy reviewer below from Edinburgh. Santa is very much real and our four year old loved meeting him a few times here.
We were amazed that after our arrival after midday to find the place so quiet the week before Christmas. You can get off and off as many rides as you want with little or no queue. Seems the Thomas Cook/Thomson hordes arrive in the morning, so I would recommend coming later in the day if you're doing it as part of a self-built tour like us. We took full advantage of this and spent two whole days at the place (same ticket). Frustratingly, the bus service (No. 8) can be random at getting here from the railway station and there's no reliable link if you want to visit Santa Village after coming here. We had to pay €12 to get a taxi from Santa Village to come here. I'm amazed there isn't some sort of regular tourist shuttle between the two places, which are really the only places to visit in Rovaniemi to be honest.
The sub-zero temperatures are not a problem, unlike Santa Village. It's all indoor. You walk down into an underground cavern and then can put your coats, etc into a large cloakroom. You can spend a fair few hours here but really if you don't have kids, you can do the whole thing in 1-2 hours.
Highlights were meeting Father Christmas (didn't pay the extra to keep the photo), going on the Magic Sleigh Ride (sort of Christmas It's A Small World) and the Angry Birds play area was fantastic.
Elf School and the Gingerbread Kitchen were very well done. The only slightly annoying aspects of the place were lack of free Wifi, charging extra for a Gingerbread cookie (first one needs to be free?) and the Elf School diploma. We paid about €82 for the three of us (it's a 2-day ticket) which should include everything apart from refreshments. Hate paying extra!!
Also loved the ice sculptures and being shown round by the Ice Princess and areas where you could write a hand-written letter to Father Christmas.
By the second day, we brought all our own food in from the supermarket and saved a small fortune for lunch. We only bought coffees here and didn't buy their hot food. Seemed a bit on the pricey side.