Nice start. Not very flashy but still nice. I understand that the game is a work in progress, and I do have a few comments/thoughts to help you on your way.
1. Try making the zoom/scroll controls separate from the mouse. It can get really frustrating when you accidentally move the play field while trying to quickly do shots. and in some browsers it doesn't grab the mouse wheel so attempting to zoom results in the page moving. Try simple zoom in/out commands in the menu, and maybe set the arrow keys to scroll the field.
2. The scroll resets when you reset the level. This can be annoying if you move the field for a reason.
3. The instructions are linked to the field which make them difficult to read depending on the zoom. Try making them separate.
4. An explanation of each ball type would be nice especially if you plan on adding more. Consider adding a tutorial level that is sandboxed so you can use any type of ball you want to see it's effects.
5. Sounds might be nice, so would some simple music, but be sure not to create a bad juxtaposition to the general tone of the game.
6. It would be nice to see the following while in the level. The current level time, the par level time, the par number of shots.
7. Either consistency in the behavior of the out of bounds zones, or something to differentiate the different types. What I mean by this is the bounding zones should either be the ball touches it and is gone, it has to pass all the way into it, or make multiple types to cover their different behaviors. Don't forget to explain these in the tutorial/sandbox level as well.
I thought it was fun, and I think it could be much more fun when the game is finished. I do look forward to it. Giving this a 3/5 and 7/10 and I hope it lives up to what it could be. Keep up the good work.