Unity has often been touted as the most powerful game engine this side of a million dollars. And while it's the leader in middleware for the iPhone and a superb development platform for stand alone PC and Mac games and for consoles like Nintendo's Wii, it has been receiving a lot of attention for its web player. The plug-in has a smaller download size than Flash and, at the time of writing, has already been installed on more than 15 million computers.
A major attraction to using Unity is the ability to author console-quality 2D and 3D games for the Web. Unity's attractive price point was a major factor in seeing early adoption by indie developers, who have been prolific, but more recently Unity has seen an increase in adoption for use with major brands by major development studios.