Well, after completing 130 or so silhouettes on Neves, it's safe to say I get the gist of it all.  Overall I'd give it a 7.5/10.

Pros: Extremely simple, yet complex at the same time.  Decent customization, such as changing the color scheme, navigation arrows and sound effects(on or off).   Good time-waster.  Ability to see achievements for each mode you've played.

Cons:  You can get easily frustrated on some puzzles, but it actually just makes you want to beat it even more.  Controlling the pieces can be a tad difficult at times, especially the smaller ones.  The increase in difficulty just isn't there while in "silhouette" mode.  There are 4 different levels, but they aren't really any different.  I've yet to try out "7steps", in which you must place each piece perfectly or else you phail.  There's also "TimePressure", which is self-explanatory.

I wouldn't mind trying out multiplayer, but unfortunately can't.  I should have the full review up by Monday.