Definitely one of the best TNG episodes.
There's just one thing that decreases my enjoyment of it: what right did those aliens have of subjecting Picard to such a (possibly traumatic) experience, without his consent? I know they were dieing out, but still, it diminishes my sympathy for them.
I don't think they did have the right, at least not objectively speaking. Subjectively, Picard has become one of them. He loves them. So, presumably, or at least possibly, he forgives them. To me, the uncertainty on this point is what makes this episode haunting.
I've never felt that this episode was overwhelmingly positive in its intent, but rather about this desperate plea of a dying world and the fact that they probably didn't have a right, but can Picard really blame them now that he has experienced life among them?
As usual, there are some things you just have to accept, such as the fact that this society is unable to leave their planet, yet can create a virtual reality device of this complexity; and the fact that it apparently only works once. But as Trek premises go, I think it is pretty solid.
Different areas of technology might advance at different speeds on different alien worlds. Virtual reality was apparently something this race was good at. Knowing the end was coming, they poured all their resources into creating this time capsule. It had a finite energy source, it would only work once. They didn't want to risk it being destroyed or wasted, so they set it to trigger immediately and automatically. Suspension of disbelief of course has to take over at some point, but I thought it was a well told story with a good sci-fi premise.