Avicii arena is pretty nice
Living in Stockholm, I find it pretty meh.
It is nice, looks good and all, but given it's spherical, there is alot of dead air, from the ice to the ceiling it is 85 meters (close to 280 ft).
Unless it is absolutely packed and a big game, it gets pretty quiet unfortunately.
And the acoustics during concerts is really hit and miss as well
I much prefer the old arena next by where the NHL teams have practiced during their stay in Stockholm. Nicknamed the Court, the oldest indoor hockey rink in Sweden, 8 000 capacity, lots of raw concrete, steep stairs and low ceiling - love it!
I haven't been to either but I can imagine it is a bit like The Forum vs Bell Center.