My wife and I love these boxes. We really enjoy almost all of the puzzles that come in them (obviously no one will love each and every puzzle), We love the fact that the website provides such great hints if we do ever get stuck on something, including the answer if you're really stuck - although if you're going through the hints, you'll likely be able to figure it out long before the solution hint. A few of the boxes are completely stand alone, but some of them within the series actually require items from previous boxes, which is also fun.
Having said all of that, the best part of the Conundrum Boxes, by far is the story that goes with each of them. Like most boxes, you enter in your answers on a website, but the website actually walks you through an enjoyable story as part of the puzzle solving. The stories are interesting, funny, and are a fantastic addition to the mystery boxes. Having tried other services, we find that the story that goes with the boxes is the primary reason we still subscribe to Conundrum over any of the others.