I am playing Shovel Knight.

I like it because it reminds me that it takes skillums to beat gamez.

It reminds me of my gaming roots on the Commodore 64, wher eevery game was impossible.

But I also like it because of what I have learnt over the last 20 years about games. Design sensibility, tactile connection, challenge, ectasy and discovery.

It keep my mind full when I don't want to think about reality.

I'm going to say the 3D Mario's.  They might be an obvious choice, but I like them so much for the level of control they give you over your avatar and for how the whole world is made to react to you.

Mario games excell at letting you express yourself through motion.  No other series has that many different animations for something as simple as a jump.  Just running around is made fun and encourages play.  The sheer diversity of options to get around encourages you to see just how far you can stretch your moveset.  Can I reach that ledge without bothering to take the clearly signaled path?  Could I skip that part of the level if I backflipped into a wall jump here?  The feeling of freedom in a 3D space is unparallelled.  Who didn't marvel as they made a full orbit around a small asteroid in Super Mario Galaxy while far jumping?  And even more flabergasthing is the fact that even after having beaten the game, you'll still stumble upon jumps you didn't know existed.  I played through all of 3D world, only to see my 2.5 year old son pull off a jump I didn't know about while he was taking his first steps into gaming.

And then there are the levels.  regardless of level design, it's a joy to see everything react as you pass by.  Trees wobble if you climb them, flowers twirl, bushes produce golden coins, ...  So disregarding the masterfull level design, the level of challenge (or sometimes lack thereof), the distinct colourfull artstyle, the things I like most about 3D Mario games is the playfullness at the hart of the gameplay, and being delighted by the little touches that liven up it's worlds.