Don't Look Back is a small plateformer by Terry Cavanagh (the author of VVVVVV) released in 2009, with minimalistic graphics and strong, abtract atmosphere. The game is extremely easy when playing normally, but very challenging at some points with speed in mind; it requires precise moves, good reflex and a nice amount of luck manipulation.

Some points worth mentionning:

1:11: the hardest jump. Only 1 or 2 frame to react. With some practice, you can tell if the jump is successful or not the exact moment you press the jump key. :)
1:42: this part requires reflex indeed. Enemies have three possible jump heights; depending of the height, I may need to stop a split second (and not more).
1:50: the main run killer. Around 1 chance in 8 the enemy will fire as expected.
1:54: it's absolutely possible to shoot the snake, but you will likely touch the ground first!
2:07: well... I somehow panicked and messed up my third shot. Sorry about that.
2:10: the abstract bad guy. He can be very dangerous and his randomness can easily ruin a run - a 25 % chance, perhaps. Here, he is surprisingly nice!
3:28: from this point I become really cautious. A bit too much.
3:58: I jump to trigger the fall of the stalactite earlier and be above it, so I can move forward in mid-air. I'm too cautious here, but it looks cool anyway.

Thanks for watching. Please let me know if you enjoyed it!