[My review looks like it's of a pre-final version, for future readers]: Very fun game, nice job! It was hard at first, but once I figured out the mechanics, I slowly got better and my scores gradually went up, which is a good sign for your game design. I kept playing it to try to get better scores on the leaderboard -- so the leaderboard absolutely worked to make me want to play more. This game has great potential, nice work.
Can anyone out there beat Starship111's score? :)
For refining it:
1. Once I play the game, the leaderboard button no longer works (it displays a popup window with a big dump of text, and the game freezes). If I wanted to see the leaderboard, I had to exit the game, re-enter, and push the leaderboard button before playing.
2. There are definitely times when the enemies come out of nowhere (seems to be from behind the orbit, though sometimes I never even see them) and end your game. There are also times when they come in so fast from the sides that there's no hope to react. I would suggest adjusting the range of entry points and starting speeds to decrease this -- as a player I want to feel the game is "fair" and that I have a chance to use my skill on each entry.
Nice job!!