It was overpriced. Came out a year later. Was going head to head with the Wii, which was a "craze" when it released. Lost a lot of traditionally PS exclusives. Didnt have a good launch line up.
But..... PS3 came back. All the "PS3 is doom!" talk stopped around 2009. In 2009 KZ2 came out and was easily the best looking game on console. Infamous came out. Uncharted 2 came out and blew everyone away, winning multiple game of the year awards. Finally PS3 had its killer app. PS Slim + price cut happened and it was finally 'affordable'. The PS3 was re-branded, and launched the "It only does everything" marketing campaign.
After being behind by about 10 million,Ps3 is now neck and neck with 360, and has surpassed some great systems like NES, Genesis, N64, and SNES. It's also set Sony up to be the frontrunner for next-gen winner. PS3 made the greatest comeback ever.