i really like dwalin. im not saying he's a good hero, because, well....he's not really. but the art is great, him just standing there with his axe over his shoulder after a hard day of hacking off orc heads.
his ability is interesting as well, though again not so useful unless you really get him buffed up on attack
He is certainly one of more interesting spirit heroes however I feel like you have to deck build around him to make him useful.(Which could said of most every hero in the game). That said, currently Spirit and Tactics splashes are still hard pressed for resources and as a theme player, there aren't enough dwarfs in these two spheres to build a proper deck.
Also I wish his ability would be more like, At the beginning of the game choose an enemy type like Orc or Goblin, when he destroys this type of enemy reduce your threat by 2. Being restricted to only Orc enemies means he is not even considered for several of the quests, which is sad.