stumbled over the Hexagon games he other day. Super Hexagon is on Steam sale for EUR 1. It's super simple and clean in design, super addictive and insanely hard. What you simply do is control the small triangle in the center and move it through the gaps in the (mostly) hexagons with a/d left/right or lmb/rmb.
There's also Open Hexagon with more options etc., but with the original you have more comparable results, because there are just a few levels and maaaaany people seem to play it or have played it. Game receives a lot of praise. Youtube has much footage…
Developer playing the hardest mode:
I'm currently playing against my cousin, I'm on the lead 24 seconds in "Hexagon" mode (the easiest difficulty), he is at 18 seconds. You need to survive one minute.
It's about having fun and going berserk.
His other game is "vvvvvv", which seems like a C64 game. Also clean design and haaaaard. Do not own it but what I have seen is just sick.