First 3 years obviously.
By November 17th 2009 (exactly 3 years after the PS3 launch in NA) we had Resistance 1&2, InFamous, Warhawk, Uncharted 1&2, Ratchet and Clank ToD and aCiT, Killzone 2, LittleBigPlanet, (I'd mention MGSIV but that's not 1st party) hmm what else...Oh yea Motorstorm and Motorstorm Pacific Rift, Wipeout HD, Socom Confrontation, Demon Souls (Sony published in Japan, Atlus in NA)
Should I continue? Sony was killing it and most of these titles were not only commercially successful but critically as well.
Digitally Sony was also breaking new ground with titles such as Echochrome, Pixeljunk shooter, Flower, Shatter (one of my fav brick breaking games, boy is that soundtrack awesome)