To my knowledge, the PS4 doesn't have that big of a library yet. A lot of the games you get for it now is also available for the PS3. I have a PS3 at the moment and I've been enjoying it quite a lot for the past couple of weeks. A couple of exclusives at least worth checking out are Hatsune Miku: Project Diva F, The Last of Us, and Metal Gear Solid 4. I wouldn't recommend MGS4 unless you played the older games first, though. If you're lacking an Xbox 360 then there are probably a lot of multiplatforms you'll be able to get with a PS3: Fear 1 & 2, Skyrim (although that's better played on the PC), Darksiders, Assassin's Creed II, Mass Effect, Bayonetta, and Deadpool. You can also get old PS One and PS2 games from the PlayStation Store on PlayStation Network if you don't want to pay extra for a PS3 that's backward compatible with the PS One and PS2.

Edit: Got beat to the first bit.