Those of you who mentioned Undertale, Superhot and Viewfinder: YES.

I would add:

- Splatoon (technically a couple of months older, but c'mon). At a time where shooters were starting to show fatigue, Splatoon was something incredibly fresh and stupidly fun with its turf battles, tower control and rainmaker.

- Slay the Princess. Sure, we have plenty of visual novels. But oh boy, this is one of a kind. Won't spoil anything, but the mystery catches you and won't let you go until you have all the answers.

- Doki Doki Literature Club. Maybe now it's not THAT creative, but I assure you when it released in 2017 it totally got everyone that played it. Worth a shot, it's free on PC.

- Screencheat. A FPS splitscreen where you can't see your oponents on YOUR screen, only on THEIRS. Now peeking at your oponents has a new whole layer of need.

Crypt of the Necrodancer is a great one.

Talking about rhythm games, I just remembered Thumper.

Also, I think both Dreams (PS4) and Game Builder Garage (Switch) deserve a mention. While they are different in terms of scope, both successfully managed to make game development a lot more manageable and interactive/fun.

Theres also BPM for rhythm games, ive never played it myself but ive been told its really good and a ton of fun. 

Think DK Bananaza is up there because of the destruction/play mechanics.

It feels like Mario 64 or Sunshine again where you can get lost just running around the world and end up sinking 30-60 minutes doing something off on your own for fun.

This game feels like something that would be demoed in a game design class to show students what proper implementation of play mechanics looks like.

This would be my pick as well; the gameplay and style is quite unlike anything else out there, so refreshing to see something so unique in this day and age.

Hmm... some good choices shown already.  Viewfinder is certainly up there as far as concept goes.  Others that weren't mentioned yet:

-Return of the Obra Dinn

 I'm not sure whether it'd qualify as a deductive or abductive investigation game, but either way Lucas Pope created something special.  Limiting info to a short audio snippet and then a single snapshot of a person dying is such a refreshing way to solve cases.

-Before Your Eyes

The pitch: your eyes are the controller / you jump ahead every time you blink.  I know I'm tooting my own horn here, but I'll just pluck this from my review: 

"GoodbyeWorld Games carries the distinct honor of producing something I've never truly played before.  Not simply a nuanced idea building upon the previous genre giants, but literally an elevator pitch that was seemingly plucked from the ether.  The way it builds around said conceit, be it story structure, visuals, or game design, to make something that feels whole is truly extraordinary.  I can understand its terse runtime and inflated price being an Achilles Heel compared to other VR options, but I'd appeal to the power of its sincerity.  Whereas scores of other titles look towards filling potential holes with content, Before Your Eyes has a more special goal in mind: making you appreciate each and every second."

Even though I appreciated getting lost in that world through VR, the concept will still feel remarkable with a PC webcam.

Loop Hero. I simple yet novel premise.