This game pisses me off...
The controls lagged which kept sending my into random directions, the gravity seemed to randomly choose whether to work or not, and quite a few times I was a single pixel away from landing when the oxygen ran out... It has the possibility of being a very addicting game, but not as it is now...
Boring
There isn't a whole lot to this game. The controls are simplistic; the various obstacles can be counted on one hand; there are only 9 upgrades, and none of them is all that great. The achievement and scoring system is well-made, but in the sense that it feels like you put more effort into that than into the game itself. I've played this game for about 20 minutes and feel like I've done everything there is to do, even though I still have one ship to unlock and Scorelord to complete. Frankly, there just isn't enough variation to keep me interested.
Some people have pointed this out before, but just in case you haven't heard; space marine and golden oldie appear to have their oxygen capacities switched.
Gravity could be alot better
This has so much potential to be so much better if you rework the gravity. Currently its effect is very "steep" (I fail to find a more suitable word): It either is applied fully, or not at all. What I mean is that once you get a certain distance close to the planet, it pulls you very strongly, making gravity "slinging" as the tutorial described something too risky to really be used tactically, whereas the planet doesn't attract you at all if even barely outside this distance. If the gravity was more linear, planets slowly attracting you even from far away, and getting gradually stronger as you neared the planet, the game would be loads more fun because gravity slinging would work much better. The game "Gravitee 2" will give you a pretty good idea of what I mean.
Also, I spent a great many attempts having only the default ship and the girly ship, and was almost giving up on the game before I unlocked 3 ships at the same time. You should spread out the requirements so that you constantly unlock ships every few turns if you play with decent skill, it would be more stimulating than going long stretches without unlocking anything and then have it all at the same time.
A final suggestion would be to add more objects other than planets. Meteors, the rare UFO and stars that are mostly too out of the way to be worth collecting are not enough.
OK but
The concept has been done before with more polish.
The gravity fields are really off, bigger planets would have stronger fields that reach out further and when exiting the gravity field you would not fly in such a straight line out with less momentum you would keep the curve and speed.
A couple tweaks and this would definitely be a good time waster.
Terrible gravity
There should be some notable way to tell which planets have high gravity, and which have barely any. Size, spin speed, colour, art style, giant glowing circles, background "air" colour. Anything. But no, to me, it seems completely random.
Also, ship upgrades would be amazing. Like, boosts to save me from falling into the abyss, landing rope to pull me towards planets, extra oxygen surplies, science upgrades for; Sun-slowing black holes, space-station creation, re-fuel stations, and nukes to blow up planets I was just on (Would give a speed boost and slow the sun down).
Power-ups for speed, slowing the sun, generating new planets (Slow travelling asteroids?), more oxygen or extra tools.
It would all be fun.
I've not completed the game, so I don't know if this is already implented or not;
Levels. End each level with a "Space warm" into the next solar system, and you can basically restart from level one but with all your upgrades and new planets, yeah?
And something that is much needed. Custom Spaceships. I'd love to be able to make my rocket pink.