4 is still PS3.
As mentioned above have a look at GT4, I've had every version so far. If youre into driving games big time, checkout 'Grid 3' . It's very similar to the old Colin McRae rally games. Takes a bit of getting used to as the controls are very sensitive. It is quite realistic and takes practice, take your finger off the accelerator too quickly round a corner and you can spin out : ( . You can have some spectacular crashes, Colin McRae style (RIP).
Seems my pay check next month will be stretched next month...
Big vote for the aforementioned MGS, WipeOut etc
The best game I've played for quite some time is Vanquish...coming from an Xbox you'll undoubtedly be looking for something to top 'Gears'..Sega have cracked it 10/10 IMO
Oh and God of War 1/2/3 - epic
PSStore allowed me to download 2 free games (infamous+dead nation) I also managed to download another 2 titles (Wipeout+LittleBig Planet) on the same console (different user)