A "classic", to the definition of Italo Calvino, is that thing which tells you something new every time you explore it. You are probably looking for something different from what that work is. Because others have found further meanings in it in the course of decades.

(And already reading this article I find myself entangled in one of its riddles.)

Edit again: and in fact, the reviewer shows to be clueless, states in clear contradiction that the movie forces passivity, places a number of questions in the review and stop short of attempting finding answers. No, the questions are there: if you are intrigued about finding the answers, that is your "privilege".

Edit:

By the way: what is «weird» to you in the «cop-out ending»? Because it is very linear if you "get" one of the main "prestiges" (after Nolan, "the thing in front of your eyes which in a way you may almost refuse to see") in the story. Edit2: and given said context, and what is drawn by the rest of the movie, the ending /is/ resolutive.