I don't know what it is about physics simulators, I had never played one before the iTouch came along (well, maybe, if you consider World of Goo one, then one), but I totally fell in love for the genre. It is simple, but it makes you use your brain in great ways, so in a way it is great exercise.
As I played Rafter, I can just say it has what you'd expect from a physics simulator. Simple, but challenging.
As I played it, the first thing I noticed was the marvelous graphics it has, very minimalistic, but very polished and well done, makes you feel like you're in an artist's sketch all the time, and I came to see that that idea is not so bad after all.
The gameplay is simple, there's a sketch space on the top of the screen, where you make either a square (rectangle) or a circle and plan (or well, if you consider yourself the lucky type, just hope and trial and error it all) the path the shape will do in the level to hit (or not) the red nucleus. That's about it, and takes me to the part I don't like. So far in the game, even though the environment does have some neat tricks in its pocket, like fans and wheels that put your objects off track, there's little setting up strategy, meaning the only thing you have to do is put the initial piece and let it roll to the objective. No setup, no nothing. A little more time with the setting up would be really interesting and hitting that red nucleus in the end would feel way more rewarding.
As it is, though, it is a really good game, it has charisma and is very polished, and for .99 cents, you really can't go wrong with this one. So if you're entering the physics simulator scene, and want something to pass up the time, I recommend Rafter to you.