Is this 20USD? I'm in the UK and I definitely consider it worth the £8.99 it'd cost me to buy it now. It's a pretty substantial game, in that you'll get a lot of playing time out of it; even more still if you download some of the excellent user-made levels available on this forum. Ultimately, though, only you can say whether it's worth that cost to you personally.
I can tell you that it's only available as a digital download, though. As far as I know it's not possible to obtain a hard-copy without making one yourself.