In order of desirability, for me at least, it's:
1) Third-party exclusives - this is the bread and butter of the Sony ecosystem, dating back to PS1. The number one reason to buy a PS system is third-party exclusives. This includes games like Metal Gear Solid, Final Fantasy VII, Castlevania: Symphony of the Night, Devil May Cry, Grand Theft Auto III, Metal Gear Solid 3, Demon's Souls, Bloodborne, etc.
2) Third-party multiplats - this is especially true of the PS4, which is basically the 8th gen equivalent of Xbox 360. Third-party multiplats generally play and perform better on PS4.
3) First-party exclusives -- Sony's first-party portfolio is a mixed bag. Some games - God of War, Ico, Shadow of the Colossus, Infamous, Uncharted 2 - are great. Others not so much. Right now, its first-party output sits somewhere between Nintendo in first and Microsoft in third.