When it comes to twitch based games, I think it's best to start with a high difficulty level and raise the stakes from there. This encourages you to keep coming back to beat your score, without feeling like you have lost a lot of time. A perfect example is Super Hexagon where you will be lucky to survive 5 seconds during the early stages with the game. With a bit of practice, you survive longer and feel an overwhelming sense of achievement.
The main gripe I have with Race The Sun is that it is too easy. You casually play through the first stage and it's got a fairly gradual learning-curve. I'm not saying I didn't die during the first couple of stages; it is still easy to make a mistake and usually a mistake is instant death. My point is that lasting a few minutes doesn't feel like an achievement. This discourages repeated plays since there's a minimum play-time before you feel engaged with it.
You control a low-flying solar-powered plane. Your craft constantly moves forward with you controlling the horizontal movement. As time goes on, the sun goes down, which is a problem for your plane since it requires the sun's light. There's a collectible item that sends the sun higher into the sky, buying you more time; so it's vital to collect these. Large objects block out the sun, casting shadows on the ground, so it's important to avoid these as much as you can.
There's plenty of objects to avoid as you are racing the sun, most of which are inanimate but some move or collapse. These elements, in addition to the grey colour scheme; remind me of Starwing on the SNES.
There are blue triangles called Tris which are another collectible item. These increase your multiplier which increases your score. There's also green triangles which give you a jumping ability. The jump gives you a surprising amount of air-time, allowing you to bypass many obstacles and collect Tris above ground-level.
Taking a hit head-on is instant death, but you can clip objects and survive. In this case though, your multiplier takes a massive hit.
You are given a list of achievements to aim for which levels up your craft. At certain levels, this unlocks upgrades for your ship. The jump ability isn't available straight away but is unlocked early on.
The level changes every 24 hours which is a cool idea. This gives you variety over time, but allows you to practice a map within a particular day in order to improve. The maps are fairly wide, and some parts of the map will contain more collectibles, allowing you to survive longer and/or gain a higher score.
It's a simple idea and is a decent game. Personally, I would have preferred if the game was harder and faster so was more based on twitch reactions. There's definitely tricky sections in the game, but it seems quite sporadic and random, rather than consistently intense.