A lot of games I play are for the "experience", more so then the gameplay.
When that grows tedious, when narrative, characters, atmosphere or themes cease appealing to me I switch to something more traditional. Games where I can drop an hour of my time and not worry about furthering the plot, or advancing my skills.
I usually fall back on classic platformers or shooters (FPS, Sidescrollers and the such), but sometimes I play beat em ups as well. I like to throw on my Sega Classic collection and just fart about in Sonic 3 or Sonic and Knuckles. Maybe play a bit of golden axe or streets of rage. I have a few Indie games that fill that niche too, like super meat boy.
When the wear and tear of actual gameplay becomes tedious, I either switch to something more narrative heavy like the Metal Gear series or legacy of kain. Some RPGs are good for this as well.
A personal preference, I can also just boot up Skyrim, oblivion or morrowind, depending on my mood, lower the difficulty and just explore the world (quests or guilds I haven't tried), try some mods (for oblivion or morrowind; skyrim is, sadly, on PS3) or experiment with Classes to create unorthodox experiences (how I discovered the wonders of pure illusion assassin).
More often then not though, I just load up Minecraft. The simple aesthetics and variety of ways I can waste time with little to no stress makes it a good palette cleanser.