The Xperia Play is supposed to be both an Android smartphone and a mobile gaming console. That is why Sony has equipped it with the "Playstation certified" label. Unlike other phones with gaming support, there are complete input devices that are pulled out from under the display. The gaming platforms that the Xperia Play supports is essentially Android, though there are also dedicated Android games adapted to the controller. Contrary to what might be expected, games for the first Playstation Portable will only run if they've been adapted for the Xperia Play's controls. This is by no means the case for all titles, but the games that have been ported so far seem to work quite well.
The Golem.de editorial staff has a Test of the Xperia Play and also supported it with a video:
Whether the device will actually be able to establish itself as a mobile gaming device essentially depends on the distribution - a single model will probably have a hard time getting other developers excited about it.