I would recommend getting this game for a number of reasons. First, you can pay as little as 1 cent for your copy (as many people did). Second, it's a great puzzle game which combines spatial problem solving with an interesting physics twist. Third, the environment is captivating, offering a unique art style and soundtrack (and you know how much I love videogame soundtracks). Finally, it doesn't require the investment of large amounts of time -- you can do a few levels and easily leave it for some other time. All of these elements combine to offer you a very unique videogame experience with extremely low cost.
Even though I already have it for the Wii (through their download content) I picked it up since it's been almost a year since I played it, so I forgot how to do most of the levels. It's really fun to go through a second time.
The "pay what you want" model is, of course, an interesting one which first gained widespread media coverage when Radiohead offered their album In Rainbows using this model a little over two years ago. Fortunately, 2DBoy were much more open about their "success": see an article here on the results of their experiment.