This can be used politically to allow you to get away with playing a powerful creature or asking for a favour from an opponent
This is better than goad, since once you are down to two players it still cannot beat your face in, and that Commander damage will add up fast with counters of growth
Its excellent removal, and the flavor is *chefs kiss*
This threatens to lead to play patterns where, once a Book is on-board, an opponent can never tap out, being forced to hold up removal should the Book player play a Haven and animate to go for the combo
The deck actually mulligans very well, and I was 3-0 in the games where I mulliganed to five
Beyond being a massive threat that can one-shot opponents, Blightsteel Colossus is also incredibly difficult to get rid of