I never get tired of online Gears of War or Fifa Ultimate Team. It seems Halo Wars 2 will be another game to play when I just want to relax.

Mainstays from a long time:
- Age of Empires 2
- Tales of Symphonia
- Advance Wars: Days of Ruin

and more recently:
- Rune Factory 4
- Splatoon

Super Smash Bros. Melee
Mega Man X
Overwatch

Racing, mostly DriveClub this gen so far.

I'd never get tired of RPGs, though more action oriented ones like Souls games usually call for a break afterwards. They take a lot out of me haha

I also come back to old-school PC turn-based strategy and Sim/Tycoon (Rollercoaster Tycoon 2 in particular) quite often. For whatever reason, I get this itch to build theme parks every few months, and nothing beats that 2D isometric simplicity. I'll probably keep playing Rollercoaster Tycoon every so often until the day I die.

I NEVER get tired of Batman Arkham games, Sunset Overdrive, Tomb Raider 2013, Gears of War 1-3, any major Zelda, Tetris, or any portable Mario Kart.

I dunno. What are Insomniac and Naughty Dog games counted as? I know Resistance is an FPS but mostly their anthropomorphic platformer TPS games. I also really like cinematic games that are more relaxing to play like Telltale, Heavy Rain, and Until Dawn

Excellent choice! Very absorbing game. I need to give it a replay. 

8-bit and 16-bit games. The genre doesn't matter. Anything else and I get burnt out and have to take long breaks.

Platforms and RPGs, might get a little burned out from RPGs, but I always come back to them.