I've had a PS3 for a few months, and for me, the only MUST PLAY games are Ratchet and Clank and Uncharted.  Both of which are absolutely gorgeous - some of the nicest art and graphics I've ever seen.

I'm pretty excited for Metal Gear, Home and LittleBigPlanet.  I think this year is when the PS3 will hit its stride with software and cheaper hardware.  The PS3 architecture is kind of ridiculous in its complexity (5 processor cores!?  Srsly?), and developers will start tapping into it and working some magic.