The short answer: it's not very good. Official support is limited to a few (mostly older) games, which only know how to work with the PSP. Meaning the resolution is the PSP's 480x272 and the right thumbstick can't be used as a true thumbstick (it can only be mapped to buttons).
You can force more games to be enabled on a CFW'd PS3, but you're not missing out on much. Even when it works you still have to put up with the input lag and the blocky image quality; action games are certainly right out. In short it's no different than remote play for the PSP right now, and that was basically a failure.