The first is that Acer has done a better job than any other HTPC vendor at addressing the couch-based input problem that plagues living room systems. The $499 Revo comes with a wireless touchpad that doubles as a QWERTY keyboard. The keyboard works better than the touchpad, which doesn't recognize your tap-based clicks as well as it should, but compared to the usual cruddy remote, or worse a full-sized wireless mouse and keyboard, the Revo 100's touchpad offers a tidy solution to a classic HTPC problem.
The second reason we like this system is that Acer has aligned the features of this system with the content Windows PCs deliver best. Its Blu-ray drive works as expected, its HDMI port, 802.11n WiFi, and optical S/PDIF jack gives you a seamless connections to your network and home entertainment components, and the large-enough 750GB hard drive stands ready to store your media. For live TV, your cable box is far more capable than any TV tuner. If you want to play games, buy a game console or a real desktop.
You can rightly argue that a $299 PlayStation 3 can perform almost the same functions as this $499 Revo 100, with the added ability to play games. Our only counter is that you can use this system to directly access the expansive variety of media formats and services available to a Windows computer. We expect at least some people will find that convenience, and this tidy PC, worth paying for.