Really, really good episode. I'd put it in the TNG genre of mind-control thriller. Similar to The Game andConspiracy. (Maybe the subgenre of possessed-Data, but that's a wide ranging thing.)
The episode starts off slow and awful. Pained bridge looks between Riker and Picard; awful Troi dialogue; cheesy planet surface special effects. Then things kick into high gear with almost no warning! The violent bridge takeover, the siege of Ten Forward, the total brutality of it all... holy crap it's intense! In fact, I would say this level of intensity is rarely, if ever matched in other TNG episodes. It's so tight with action and suspense that there's no room for stupid glances or meaningless fades to commercial.
The other thing Power Play has going for it is the mystery element. What happened to the away team? Who are these entities? Are they really the crew of the Essex? What's their ultimate plot? What trick does Picard have up his sleeve? A+ work there.
And of course, the rule of escalation is followed immaculately. Every solution the crew tries backfires, until they run up against the last possible idea (and that entails a point of no return).
Anyway, hadn't seen this episode in roughly 20 years until tonight. Thought I'd go on the record about it.