To anyone that's bought one, how are K'Nex's blocks?
Not bad, but I'd expected better. The bike falls apart if you put too much downward pressure on Luigi, but the kart stays together rather well. The jets/mufflers on the back of the kart might fall off, but the kart itself stays together better then the official LEGO Toy Story kart that has a similar pull back function. The K'NEX kart seems to sit at a strange angle, Mario has to lose his legs to ride it, and the stickers don't cover as well as the picture, but over all I like the sets.
The instructions, stickers, and design choices are inferior to LEGO. For example, K'NEX uses two 1x2 pieces instead of a single 2x2 piece that would have been easier to build with and resulted in a stronger structure. LEGO has always had better instructions in my opinion and with there recent more modular instructions my four-year-old girl can build 100+ piece sets, but she couldn't follow the K'NEX instructions and I must admit that I had a little trouble with them.
On the plus side, the K'NEX Mario and Luigi figures are in the correct proportions to their characters which would never be possible with LEGO minifigs.
If I had to rate them I'd give the kart a 4/5 and the bike a 3/5.