I know it got a lot of "meh" press but the first Watch Dogs was a lot of fun for me (although perhaps just because it was the first 'new' console I'd gotten since, like, 2008) and something I look back on fondly. The 2nd is probably 'better' but will probably cost a bit more.
Agree with TS on The Last of Us.
I can't remember if Dishonored is a PS3 or PS4 original but it's great. A lot of people recommend Overwatch but I think it's still quite full-price (same as GTA 5, although that's a little less now)
In terms of just general fun rather than big-story games: Rocket League, Disc Jam and Fortnite are all either massively replayable or free. I wouldn't pay for Disc Jam but I would've paid for Rocket League, had I not got it for free with PS+. There's loads I've downloaded for free but never played, Bloodborne being one that's supposedly amazing