Power Sink appears to have a good effect in that if a player does not pay the X cost that they end up having all of their lands tapped for the remainder of that turn. It can be used as a decent trick, though, and force players to have to pay a cost that they really don’t want to. It’s certainly better than Spell Blast, which just spots a spell by paying 1+X where X is the converted mana cost of said spell it’s countering. At least Power Sink is a permission-based spell that can have a potential negative effect for the owner of the spell being countered.
It’s certainly not one of the best permission spells around, but it’s certainly not one of the worst. Most times, though, cards like Counterspell, Cancel, Dissipate, and Dissolve are strictly better.