Two words: Patience Simulator
Let there be no doubt: this game will wreck you. That's also part of the reason why Super Hexagon is so popular, because it is one of the few minimalist games that test your raw skill, and is not afraid to punish you for the smallest of mistakes.
The level design is fairly linear, besides the frequent break-off points that let you choose which semetrical path to follow; these are fairly important in the later levels, where positioning and pre-planning is important for your continued survival. In other words, Super Hexagon will only allow you one or maybe two methods in which to pass by any particular obstacle, and that's it. It's your job to keep up with the ever-changing deluge of shapes rushing to crush your tiny triangle.
The gameplay mechanics are fairly solid, and I haven't had a situation where I can blame my death on the game, but rather on my lack of speed and pre-planning. The only thing I can tell you is that you will die. At lot. That's part of the beauty of Super Hexagon, it's the challenge that forces people like myself to continue the onslaught of shapes, and anything less than victory is an insult; make no mistake, this game is winnable, but you'll have to dedicate large chunks of your time in order to gain the necessary reaction time to complete the levels.
I would estimate that it would take upwards of 20-40 hours for an average player the beat the game, but that's just a guess. Regardless, after all the deaths and failures, final victory has never been sweeter, and you may proudly display your achievements on your Profile page to show to the world just how badass you really are.
So enjoy the game, and make sure to stick with it; if you're not playing this game and learning from it, then it's playing you.