Tiny Heist, by Terry Cavanagh (VVVVVV, Super Hexagon) is a simple but addictive little stealth game which takes some of the genre's most established ideas and whittles them down into what feels like Metal Gear vs Pac-Man.
There are guards with search patterns, cameras tracking movement and locked doors, but overcoming most of these is as simply as just getting behind them and knocking them out. Just like a fancier stealth game, then, only without all the fiddling and save spamming.
The guards will even chase you if you alert them.
You can, and should, play it here.