Phosphor isn't as rich as Half-Life or Far Cry, but it's a smooth experience, and it's set up for network team play. Which is good, since the game world is too small for a satisfying single-player experience (although the in-game bots are pretty competitive).
With network-delivered games, there are two big advantages: First, new levels can be delivered as needed, over the Web, making the typical download process for a game nearly invisible. Second, since the game runs directly in a browser, you can play anywhere. Like at work. You didn't hear it from me.
Phosphor
Category: Game
Developer: Rasterwerks
Stage: Open beta
Cost: Free
Special recognition: Technical Achievement