Some things that make it instantly better than purchasing iPhone apps from your computer:
1. This web interface is lightning fast, iTunes is horribly slow. 2. You get to use the standard browser controls over the random clutter of controls in iTunes. 3. Pressing "install" installs to your phone without having to plug it in, or sync, or worry about losing your shit.
I think it's a great first iteration, and it's definitely something that has been a long time coming.
From your desktop web browser?
This is an important point. Every time I have to use the iTunes store I'm annoyed at how sluggish it is, how poor the search is, how odd the navigation seems to be, and how much I miss having tabs.
The tabbed interface for the app description/screenshots, user reviews, update info and permissions info is patently superior to the messy iTunes app pages.
The Market is really orders of magnitude faster than iOS's app store, too.