Killzone shadow fall.
But I only have had my ps4 for 2weeks and ahev barely played anything else due to exams.

Even the screenshots from this game look amazing 

For me it is without a doubt Super Mario 3D World.
One of our multiplayer files has over 2500 deaths, it's just so much fun. As much as I enjoy the 3/4-player experience I think it really shines in single player and 2 player co-op. Besides the multiplayer camera there isn't really anything I don't enjoy about the game. It's too bad they weren't able to incorporate a system where the gamepad would follow one character and the TV screen another.

The only game I've played on other 8th gen consoles is FIFA 14 on PS4 though, so my selection of games is rather limited.

SM3DW= WiiU
KIU = 3DS

Console?

Super Mario 3D World

Handheld?

Three way tie between Fire Emblem: Awakening, Pokemon Y, and Link Between Worlds (still need to beat this).

ZombiU is definitely my favorite this Gen ...( just have a WiiU atm)

Killzone. I don't care what anyone says I love the more open environments and all the extra strategy the owl adds to the combat. I wish it would have health packs, more than 2 weapons at a time, and weapons with character that were all significantly different and sometimes silly that could be upgraded (since it's in the future they could get away with a lot more before breaking the story) a la Resistance 3 but you can't win em all...unless you're Resistance 3. Now I just wanna play through more Resistance 3 thanks a lot CHRIS!

Its amazing to me the number of people who name last gen games that have just been ported over like Assassin's Creed.

Mario 3d world no contest

handheld

Ocarina of time 3d if it counts.