PixelJunk Eden is a pretty unusual game. The gameplay is somewhat open, in that although there is a goal in each level (search for and collect the "spectra"), there are a few different ways you can approach it. You can just jump around as much as possible, searching around for the spectra, fleeing from the occasional enemy, and sometimes making a mistake that lands you back at the bottom of the level. Or you can focus on collecting pollen and building the branches - playing it safe - until you just happen across the spectra naturally.
The game is (intentionally) slow paced. Each level is basically the same as the last except that you meet new enemies and unlock new abilities as you complete each "garden". The soundtrack has a very "indie" feel to it, but it's decent - just a little repetetive.
It runs decently on my 4 year-old low-end laptop that only runs TF2 at 10 fps. The game is clearly designed to use a mouse (some of the abilities require a scroll-wheel), but I have no problem playing it on my touchpad.
In the end, I'm not entirely sure why I enjoy the game, but it serves as a good way to take a short break from work/studies and relax. It's carefully designed to be moderately engaging but almost never frustrating.