Writing about web page http://www.sunflat.net/en/games/sfcave.html
This game combines such ridiculous simplicity with infuriating addictiveness that I'm almost embarrassed to recommend it. There's only one control – mouse click – to master, and a game tends to last no more than thirty seconds or so. But it is weirdly compulsive.
If 2D strikes you as too wilfully retro, there's also a 3D version of the same thing, although despite 3D being on the face of it cleverer, I found I enjoyed the 2D version more. But that's probably just my age.