So, I've been thinking over the last few days about the main campaigns' replay value, and to be honest, I'm not sure it's possible to replay it and enjoy it. Don't get me wrong, I LOVE Portal 2, but it's a puzzle game. You're supposed to think with portals, trial and error, experimentation or maybe even just looking around and pushing buttons, until you finally find the solution to the puzzle, which is very satisfying once you find out what to do. While this is fun, this is what gives the game little to no replay value. Once you know how to solve the test, the game becomes a walk in the park with your new puppy. You know what to do to solve it, which takes away the problem-solving aspect of the game and ultimately the funnest part of the game - the satifaction. As for the story, it's truly a great one to behold. Building on the simplistic storyline of the first Portal game, I found Portal 2's story to be much more entertaining. With new characters and settings, I loved the story from beginning to end. Hearing GLaDOS' voice when she awakens is truly chilling, the way she puts emphasis into her tone of voice and personality. I found Wheatley to be slightly annoying, but I was saddened when he went all crazy then I had to throw him into space. As for Cave Johnson, I found him to be a very colourful character. Oddly enough, I found his speech about combustible lemons to be slighty inspirational, and he does a great job of narrating the tests through his pre-recorded messages, as I would get the occassional laugh or two. Overall, I would say that there is replay value in Portal 2, though you should do for the story only. If you know what to do already, then there's not much point in doing it besides playing through the story line. Community Test Chambers are your best bet if you need an excuse to replay it. TL:DR - If you're gonna replay it, do it for the story. It's not any fun if you do it for the challenge and you know what to do already.