It worked very well for my startup in the restaurant reservations space. Our objective was brand awareness in a specific city and our target audience were journalists and social media influencers in general.

We also used it to target those who were already using competitor's services.

It is not set and forget, though. You have to tweak it constantly and, as other have said, it works better for "soft actions", like "likes" and email subscriptions.

You can't compare it to adwords, it's a different beast entirely.