One other subtle strength here is the degree of control you can have over exactly when cards are milled, and how many (assuming you have painlands or other unrestricted self-damage sources)
If you can get this token it's going to feel pretty awesome, but there are lots of board states where it just isn't possible
In Modern, it has led to a resurgence of Yawgmoth decks, while in Legacy its showing up in Cradle Control
Number One I've been playing with squirrels a long, long time, and no card has won me more matches in those decks than Squirrel Wrangler
Dark Ritual is the reason why cards that add mana to your mana pool are called rituals in the first place
Early game engine commanders like Rhys the Redeemed or enchantment-focused decks like Sythis, Harvests Hand and Tatsunari, Toad Rider might survive a few more turns because your opponents dont want to give you the card advantage when they destroy your commander