I've been playing fantastic contraption 1 for over a year. Now that FC2 is here, that playtime could very well double. The level editor is superb compared to the original. It is much more user friendly and allows for a much broader range of concepts.
The design builder is also very good. With the addition of undo and copy paste, building is much quicker this time around.
Magnets as well as joints have a few quirks, but generally it doesn't reduce much fun from the game unless you are a hardcore contraptioneer.
Compared to the first, the graphics are a little bright for my tastes, but are easy to get used to.