It’s designed to be fast and light — and it’s definitely a Lite version in that it doesn’t have Google Reader syncing, tabs, Combined View and other features you might be used to. It does the basics, for folks who like their apps light and lean. (There will be a full version of NetNewsWire 4.0 with Google Reader syncing and other features.)
A couple of posts on inessential.com go into more details:
Also see the The Making of NetNewsWire Lite 4.0, a photoset on Flickr.
Here’s a screenshot — click it for the larger version:
(There are more screenshots on its App Store page.)
Edit: 03/12 This application has been removed from the Mac App Store.