I don't know what it is about the Mistlands but it just misses the spot for me somehow. I don't mind the mobs at all. Well I do curse when a 2* seeker lands on my head but the biome itself is just meh. If I had to rank the biomes for my faves it would be a little like this

Plains>=Mountains>Blackforest>=Meadows>Swamp>Mistlands.