The Borg get all the headlines, but when you really boil things down the Romulans were the best villains that TNG ever had. They were the consummate bad guys - intelligent, devious, and human enough that we could understand their motivation. They also brought out an edge that wasn't always present in the lovey-dovey TNG universe.
My recollection of this episode was that it was very good, but overshadowed by its sort-of-sequel "The Defector". While that is probably true (I haven't gone back to "The Defector" yes), this episode was better than I remembered.
The story about Geordi and the Romulan centurion stranded on the surface of a forbidding planet was quite good. Geordi wasn't a favorite character of mine - while likeable in the role of the chief engineer, he was just too nice and lacked an edge. Still, it's fun to see him first struggle against the elements and then convince an opponent to cooperate for the sake of survival. It's also an interesting contrast between the way mankind would like to think it behaves (Geordi, the Federation) and the way it often really behaves (THOSE DEVIOUS ROMULANS!).
But really, the meat of the episode lies in Picard's psychological warfare with the Romulan Commander, Tomalak. Tomalak was one of the best villains in TNG, though unfortunately he was used only sparingly. This story kept me on the edge of my seat, even on repeat viewings, and would be developed even more effectively in "The Defector".
Finally, a note should be made about a superb third subplot -- a relatively brief one -- regarding Worf's moral dilemma. While it takes up only a fraction of the screen time, it adds a fine psychological dimension to this episode - and unlike most TNG subplots, doesn't settle for a happy ending.