I'm not a huge fan of Lego's Ninjago line (it reminds me of the Power Rangers), but my 6-year old son LOVES it (probably because it reminds him of the Power Rangers), so we recently bought him the Kai's Blade Cycle set. It's a giant red motorcycle with four "arms" that extend at the press of a button. The set also includes two minifigures - Kai ZX (my son assures me this is different from the plain old Kai, but is vague on exactly how) and a bad guy called Rattla. There's also a little platform that holds a staff with a unique hypnotic-style piece.

Complexity: The set has 188 pieces, and once I saw that most of them were Technic elements, I knew I'd be assembling this one for my son. The instructions are clear as always, but the more complex Technic pieces tend to be more difficult for younger builders. It took me 30 minutes to assemble the bike.

Playability: It's a ninja riding a giant red motorcycle! Yeah, this one is getting played with a lot. I love that it comes with a bad guy as well as the main character. I think Lego is stretching things a bit to call this a "transforming" set when all it does is extend a bit, but it's still a neat feature.

I still prefer the City and Kingdoms sets, but I have to admit Kai's Blade Cycle is pretty cool. It's a neat, affordable addition to the Ninjago line, and one that my son definitely enjoys.