One of the greatest endings to a game I have ever played, and quite possibly the highpoint between Portal 1 and 2, which says a lot. On replay, however, there is a disappointing lack of story content through the first several test chambers. The story only gets interesting in the back half of the game, so for those already familiar with the mechanics of the series, the first several chambers seem to drag on a bit. Nonetheless, Portal is an incredibly tight package of a game that I couldn't put down.