I just bought this for my five year-old son. He loves it, and plays with it for hours at a time. Those who say it falls apart easily after 2-3 hours for assembly aren't lying. This has been a great opportunity for me to teach my very battle-loving son that not every toy can just be knocked down! Once he understood that it was too much work for mama to put it back together each time, he has been great with it. Using glue on the walls would probably solve this, but I like that he HAS to be relatively gentle with it. That said, even if he were rough with it, nothing on it would actually break. Playmobil stuff is incredibly durable.
Some of the details on this castle are amazing. I particularly enjoyed the "toilet," which is a hole cut into a ledge in the castle wall, just like the real castles used (ew!). My son thinks it's there so one can poop on one's enemy, which would be a great battle tactic... The flags, torches, ladders and furniture are all great. Of course, the breakaway wall is super fun (and if you buy an additional "big" canon, it will actually knock it down, and you can get more enemy knights with it, which is a plus). The bucket for lifting things has been popular, as is the trapdoor. He likes the contraption for dropping rocks over the wall. There's even a chandelier that can be raised and lowered! The fact that there's a queen has kept his stepsister engaged in playing, too (the queen can also hold a sword, which makes her even more fun).
Playmobil also makes many "single" knights, which can be bought for just a few dollars each, adding novelty at a future date. I particularly like the carrying case with a knight, horse and many accessories. All in all, this is the best toy my son has had, and I anticipate being able to add to it with occasional new knights over time to keep it fresh and fun for years to come.