Hmm, not exactly convincing. Leopard brought stuff like time machine, this smells more like a big service pack. I mean, OpenCL and some of the central applications running 64-bit? Better Quicktime and a new Safari? I don't even use QT and Safari. And it's $29? Too little to be too much, but still a lot for a service pack.
And there really has been a lot of re-engineering, most of it focussed on making things a lot faster and smaller.
I think Apple deserve our thanks for actually making performance and improved footprint an explicit goal of a major release, rather than larding on new feature after new feature in some kind of misguided feature war.