It's a start. The best advice that I could give would be...
1.) Pickups: more objects, maybe there can be objects that are worth two or three points.
2.) More variety. You could have a set number of red dots to get in each level. Also, change the layout (and background) of each level so that the player doesn't get bored of staring into the same screen for hours on end.
Uhh, I guess more variety is the most important thing, whether it be different objects, levels, time limits (perhaps for the whole level or just to get to each object), maybe the green dots speed up as the levels progress, etc. I hope I was at least a tad bit helpful. Good Luck!
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