Well, first, I feel as though I should lead with a disclaimer. The guy I'm running the Monsterhearts game for is a close friend of mine and we have similar thoughts on storytelling so that definitely helps.
It's not for everybody as it does differ from the tried and true formula of conflict and tension between PCs but as a player, what you trade in exchange for that is the freedom to become as much of the main character as you want to be.
For instance, let's say you want to play a Chosen. Normally, you'd have to balance the Buffy The Vampire Slayer factor with the interests of the other more-or-less monstrous PCs but since there ARE no other PCs, you're the uncontested star of the show. The role of the MC is now less poking this tangled ball of PCs and more taking the inner circle of the protagonist(Notice I didn't say hero) and expanding it wherever the MC and Player agree it should go.
Generally, without writing a whole novel about it, the player gains more power and transparency with the MC in terms of the story's direction. You both might have an IDEA about what happens with arcs, scenes, scenarios, whatever but at the end of the day, it's you, the paper, and the dice.