Some nice work there. A few more thoughts.
1. SPACE BAR and LEFT-CLICK: It would be better for anyone using a mouse (or mouse emulator) if you could use LEFT-CLICK to play. It would be more intuitive for such users. I do like that once the game has started, it's easy to RESTART and play again. That should be the same for Space BAR, and Left-click use. You shouldn't have to move the pointer to do that.
2. Front end MENU is all text: Same problem as before for people who cannot read English. Possible solutions: PLAY symbol could be a triangle on its side pointing to the right. SETTINGS a COG or spanner. EXIT a European door exit sign symbol. CREDITS perhaps a question mark, or something better.
3. ESCAPE KEY. Requiring this key forces a switch user to either have access to an On Screen Keyboard (normally using a mouse-emulator to click on it), or a helper. Might be an idea to also have a back-arrow symbol to get back to the front menu screen. Additionally, ESCAPE does not seem to work at the GAME OVER screen, which is confusing.
4. FULL-SCREEN. Once you enter this, how can you exit it, if you don't have access to the ESCAPE key?
5. MASTER VOLUME. This is redundant as you have sliders for SFX and MUSIC. I'd recommend defaulting to 50% as it's too loud in competition with the SFX in my opinion.
6. SFX. In game, when you press SPACE BAR (and hopefully soon left-click), I'd recommend it plays a sound effect. This will help users realise that what they've done has taken effect, alongside the visuals.
7. Making sense of the game. I think that the stars are good, and black holes are bad, becomes clear quickly in the game. I would say that the dark holes are not that easy to see, if your eye sight is not brilliant. Maybe a HIGH-CONTRAST option might be an idea?
8. Improving the gameplay further. Maybe a audio-visual reward for certain targets. 10, 20, 30, 40 big one for 50 and so on?
9. SPEED. If possible, I'd suggest 5 divisions, with SLOWEST being even slower than the one you have.
Best wishes,
Barrie
OneSwitch.org.uk