I have all three systems. Unfortunately I don't have the funds to get all the games I want to get for them. Nor do I have the time to play them like I want to.
That being said, If you have the time and money, yeah its worth it. The PS3 is quiet, it plays blu-ray, it connects to the internet, and a host of exclusives..
Demon Souls
Metal Gear Solid 4: Guns of the Patriots
Heavy Rain
Killzone 2
Lair
God of War 3
Folklore
Little Big Planet
Ratchet & Clank Future: Tools of Destruction
Ratchet & Clank Future: A Crack In Time
Resistance: Fall of Man
White Knight Chronicles
Warhawk
Uncharted: Drake's Fortune
The ability to play any PS1 game.
Upgradable Harddrive, make it as big as you like.