Okay, okay, I'll be the first to admit that Twitter's Windows 8 app isn't quite as seamless as the social network's Web client. (Why, oh, why do I have to click through to a tweet in order to RT or favorite it?!) But that said, Twitter's central stream-based design works very well with Microsoft's modern-interface concept, and the app is much easier to poke and prod than the Web version.
The Twitter app also ties in well with Windows 8's nifty extras. The ability to Snap the app to the side of your screen and receive system-wide notifications is alone worth the price of admission—especially since said price of admission is a low, low $0.