It's a good start, much like the PC version once was.
For being little more than the basic framework of what Minecraft's become on the PC, it's very solid, and still similarly addictive. It's just bare bones, so if you really want the full Minecraft experience on the iPad, you're going to have to wait.. but, should probably still consider buying it, at least to show your support, helping increase the likelihood that it will continue to be developed into something much more like what we've seen on the PC. It's just a matter of time, as long there's enough interest in it, on this platform, and from what I can tell, there is.
Knocking it because it's a long way from finished though, is just ignorant. They're calling it an alpha release, and it says right on the app store page, "Version 0.2.0" It's got a ways to go, but maybe they should be a bit more explicit about that, right there on the App Store page.