Certainly one of the top family parks in the world, not the level of say a Disneyland, but for Europe it's excellent. And don't miss the traditional and very cozy Julmarknad in November/December.
Helix was the best ride. Got there at 11am to buy the Alt-I-ett tickets (all rides included) and for ~475kr it was definitely worth it. Helix had a 10-20 wait time. Mechanics not worth though.