Building Zelkriph was the real turning point for me; to be honest, I looked at the instructions and thought "whoa, this guy is a real mess. Then I took about an hour and built the real terror of the skies.
I couldn't get all the colors right, such as the fin segments that I only had in azure, and I actually didn't have the right gunmetal parts to represent the hind legs or a few parts of the right wing, but this set is still gosh darned awesome any way you slice it. Awesome. Awe-inspiring.
The build is complex, entertaining, engaging; the gear function is more laterally compact than we've ever seen it before, and it almost feels as though I'm building one of the 2001 Rahi. The monster has definitive breadth and is filled out well; the armor covers pretty much every technic cluster, and it looks like a bat. It's a tedious build, which is the way I like it. 
The instruction were a bit unclear at times; was that a 4-angled technic connector on the wings, or a 3? Is that a 3M double axle-single-pin connector, or a double-pin-single axle? Some of the colors were a bit hard to decipher, and I was working in a relatively dim room with an iPad on full brightness. There's also a ton of silver; way too much for a Jungle set, IMO. As a side note, and a bit of a nitpick, the Kaiju fins as ears are facing forward on my copy; I think that they look a lot better like that.
Bravo, even more than usual. My reviews of all the generals are still coming up. 8.5/10