The must plays. (Some depend on if you played the last gen version of the game or not)
Tier 1. Must Buys
Bloodborne
Witcher 3
Dragon Age: I
TLOU:R
Infamous: SS
MGS5
Tier 2. You wont regret buying (most can be found for cheap too)
Shadow of Mordor
Dying Light
Far Cry 3
Diablo III: ROS
Driveclub
Batman: AK
Woflenstien: TNO/TOB
Tier 3 Games I enjoyed a lot, but might not be for everyone
Destiny (would be higher, but if you have a major backlog to get through you might want to avoid it... can eat thousands of hours if you get sucked in)
SW BF
COD BOIII
Disgea 5 (make it tier 1 if you like SRPGs, its really good)
Tales of Zestria
The Order 1886 (if you get it for 9.99, get it. Takes about 10 hours to plat and it will show you what PS4 can do graphically)
FF14: ARR a great MMO, that plays amazing on the PS4.