First of all, I don't think it will help to mention all the things that you've already decided to change, so I won't talk about balls getting stuck or music.
The levels you've also said you'll change, and though I'm not an authority in level design, the three levels I was able to play felt unispired and strangely... claustrophobic in their design. The blocks for the walls, as well as being glitched, were a little chunky and took up a very large portion of the level. I spent half the time waiting for the balls to get back into a position where I could hit them again.
The game mechanic itself is interesting, but it's difficult to see the point during the second and third level where the centre paddle was basically against a wall for the most part, and there was little need to throw it out to catch the ball as it began to fall. I would suggest more focus on the up/down paddles, as they were more interesting to try and control, and possibly better placement. Probably make them smaller too.
It's worth noting that as soon as I started, I had absolutely no idea what I was doing. I eventually worked out that I was supposed to control up and down paddles, and as the balls hit the rainbow blocks I got more points, but I never quite fingured out a relationship between the progress I was making in the game and the point where I could move to the next level. The "onto the next level" seemed to pop up at a random interval in time. Was I being timed or something? I noticed later a brief mention in the side panel, but not all people read those (me neither, it seems), and it didn't explain all the rules. Perhaps a page at the beginning of the actual game just to briefly iterate the rules for the tunnel-visioned ones, such as myself.
When you're redesigning the levels, think about the atmosphere you're trying to make. Is it lively? Mysterious? Retro? Futuristic? Is it set in space? A fantasy world? And then you have to take the gameplay into account. Does the gameplay match the theme? You said before that you were thinking of taking cues from the Gummi Ship levels from Kingdom Hearts, and that would fall under the "lively" category. You should think about the atmosphere when designing a game to keep with the theme. Make sure the colours aren't too washed out, but neither should they be to colourful, or painful to view. I got the feeling the colours were a little washed out in the current version, and I sensed were heading for a space theme. That could be why the music and the atmosphere didn't quite match up with the gameplay
Also, just as a side not in the sound department, you might like to think of some sound effects for the ball. As long as it's not too annoying or intrusive, I think it might liven the atmosphere of the game up a bit. I'm not sure how well it would work with the music, but if you found the right sort of sound for the game, I don't see any reason why not. Given the appropriate sound effects, you could even do away with the music altogether. Just a thought to consider.
Otherwise, a fairly good indication of a possible gem. I think you should work on refining the game machanic a little more first, then the level design, and then everything else should more or less fall into place from there. Good work. I was never any good at Game Maker, I hope you have more luck.
