Snowcloak is one of the most fun dungeons in the game.

Qarn has some really nice boss mechanics.

Sastasha is great but the DPS check on the 2nd boss can be pretty tight and the Kraken takes 500 years to kill.

Think they're all pretty sweet tho. Only real argument I could see for anything being "overtuned" is the 2nd boss of Sastasha, though I think it's still doable as long as you understand how it works and save CDs for the shots.