AndrewC: I've gone ahead and bought the game. Now let's see if it keeps me interested long enough :)
The most rewarding part of it is in the sculpture, I find. In conceiving something, and seeing it to realisation. If this is not your style, then the gameplay elements probably aren't robust enough to keep you really engaged. The logic elements, redstone, are neat to play around with, but slow and difficult enough to build that it's annoying to build complicated circuits. There is also a limitation in input/output which inhibits it somewhat.
Nonetheless, there is always entertainment to be had - and satisfaction in seeing a structure work/turn out as designed.