Bit of mixed feelings on this one! For the most part, it is a rather cute and amusing game which, while not having the best first impression in the way that its a bit overly simple and crude in terms of graphics and mechanics, it does pick up the pace in the later levels with some interesting challenges and variety. Also, I did like the little touches the game had, such as the amusing way the bird would react when the rocket would get close. Cute stuff!
Unfortunately, I did find myself that, the longer I played it, the longer I didn't want to play it again because of the life system and the fact that you need to start all over. I understand what you're getting at with the way it is designed, where you fight to see how long you can last until you run out of lives, but I wish the game was just a standard level progression with no lives or anything like that. Basically I'd like to just be able to go through all the levels and continue where I left off without needing to worry about starting all over and going through all the boring no-challenge early levels to get back to the good challenging stuff at the end. Perhaps I'm wrong in wishing for this as it might make it too easy, I dunno.
Apart from that, there were also some other minor nitpicks like how I felt the spaceship was a little too simple (I really expected it to have more analog turning controls instead of angle snapping, though I guess that wouldn't work with the cramped levels) and that I felt you should say that you are able to hold the jump button when you hit the springs to jump high (the controls say press which implies you have to time it, which you don't have to luckily since the game is nice).