The Enterprise is swallowed into a mysterious void, and every likely means of escape turns out to be a hopeless cause. It's surprisingly intriguing and entertaining, much more so than I remembered. The early stages might best be described as "sci-fi procedural," where the story elements are played for their mystery value and overall atmosphere. The episode doesn't get overly worked up about the strange things going on, but simply observes the Enterprise crew as they try to solve the dilemma. This laid-back approach (with danger implied rather than explicit) somehow makes the episode more effective.
All the usual solutions fail: They deploy a beacon, travel away from it as far as they can, only to arrive upon it again, as if they were running in circles. When holes in the void appear and offer an escape, they then suddenly seal at just the last moment, as if on purpose. When the Enterprise's sister ship, the USS Yamato, appears, Riker and Worf beam over to investigate, but find an empty vessel and a variety of funhouse tricks and illusions. This leads to a humorous sequence where Worf gets fed up and goes on a rampage: "This ship has one bridge! One bridge! One Commander Riker! One bridge!" And Riker has had it too: "Let's put all this technology to work and get the hell out of here!" It's fun to see the TNG characters lose their cool.
Ultimately, the Enterprise crew realizes they're being toyed with ("Rats in a maze," Pulaski observes) in an experiment by a superior intelligent being that calls itself Nagilum (Earl Boen, obscured by visual effects). What doesn't work, alas, is Nagilum himself; as alien designs go he's an exercise in stunning hokiness. Furthermore, his revealed agenda — to understand human death by killing half the crew — strikes me as manufactured for the sake of jeopardy. If Nagilum is so smart, why does he need to kill half the crew to understand death? Nagilum's first victim would've been Wesley — if not for the fact that Wesley is conveniently away from his post during only the scene where someone needs to die. Standing in for him is a Black Guy in a Thankless Role, whose sole purpose is to be killed. This red-shirt death is so blatantly transparent that it possibly outdoes every red-shirt death on the original series.
Not willing to be killed one by one, Picard and Riker arm the self-destruct sequence. Awaiting The End, Picard has a fascinating speech on the philosophies of death that's an example of Trekkian dialog at its finest. It's enough to convince Nagilum to release the ship, which only fuels my belief that his whole death experiment was a pointless enterprise.