Mouser: The reason the controls are wonky is because of the way Game Maker works. It's so "user friendly" that it doesn't easily (for a beginner/without going into advanced mode) provide a way to change the object's movement direction without stopping the other direction. As you say, getting the physics and gravity working properly wouldn't be too hard if you were typing in regular code, but the way Game Maker organizes everything, it tries to simplify it to the point where it makes simple things (for somewhat experienced programmers) kind of difficult to do without going into advanced mode.
Wreckedcarzz: My opinion on the game is that with the current control system you should get rid of gravity completely. Once you get a more natural movement working then gravity can come back in. I think that what mouser means by acceleration is that when you press a direction, the ball doesn't immediately start moving at a speed of 10, but increases its speed in the direction you're pushing by a smaller amount as long as the button is being pushed until it reaches a max speed. This would be something like speed += 2 (or speed = speed+2). I just opened up Game Maker and took a look at it and what you need to do for proper acceleration is click the little "Relative" box when changing the speed. That will make it whatever it is plus the number you set.
And also what I think mouser means by not having the horizontal movement affect the vertical movement is that when you are moving to the right and you press up, you go straight up and are no longer moving to the right. More natural movement would allow the ball to keep going to the right while also starting to accelerate upwards. Unfortunately, I don't know if that is possible using the little Game Maker blocks for changing movement. You might need to put in some custom code--which you can actually do in Simple Mode (I think).
Anyway, I think that it might be useful to have a couple of tutorial levels that explain what the objects do in the game rather than just linking to the help file, which most people will not read.
Keep working on it.