Yeah, Witcher 3 is definitely a great game to get. You don't really need to know everything from Witcher 2 or 1, and if you want there are summary videos on Youtube for that as well.
Rocket League is a great start on the PS4 for games. Awesome and addicting game.
If you're into the whole Black Ops Zombie thing, you might as well wait for Black Ops 3 that comes out in a couple months.
Then, there's always Dragon Age: Inquisition if you like RPG's, but that's similar to Witcher 3.
Bloodborne is one of the PS4's big titles as well, and an exclusive. It's a trial and error type game where you take down bosses and other enemies in a dark world. Looks gorgeous as well.
GTA5 is always a good choice, if you haven't played it then that's even better. The next-gen edition for PS4 and Xbox One is a decent upgrade over the other consoles. If you played it a ton on the 360 though I wouldn't bother.
Destiny is pretty good if you were into Halo and other games like Borderlands. If you've never played Borderlands, then I would highly recommend the Handsome Edition for PS4. Comes with Borderlands 2, the Pre-Sequel and all of the DLCs. Possibly 1 as well but I forget.
If you're into driving, then Drive Club is pretty good, and there is a PS Plus version you can try out for free.
It's kind of hard to give you an RPG, since there aren't many on next-gen yet. At least not of the type that Secret of Mana or Shining Force are. Final Fantasy 15 comes out in awhile, so that's a huge plus in that regard. But I've been waiting for that game for 10 years.
If you've never had a PS2, or never played Final Fantasy 10, then there's the FFX HD Remastered. Looks quite a bit better than it used to on the PS2 and is in glorious HD. It's an awesome turn-based FF game.