I'm liking it.
A couple of notes(mostly ridiculous pet peeves):
Thanks.
I don't like all the settings inside of graphics, that type of stuff should be auto set based on screen size/density.
This was put in due to feedback, the default setting is auto which calculates what I feel to be the best fit based on screen size.
Shooting seems a little sensitive. I'd also prefer the cue being shown bedhing the cue ball itself instead of where you touch. (This might be a problem for when the cue ball is sitting on the rail).
I don't actually show the cue, just an indication of where you have dragged (this is necessary, without it it's horrible to cancel your shot or reduce power). If I show the cue behind the cue ball I think it gets visually messy, if it's rendered flat it doesn't fit with the either the balls and table or my HUD. If it's rendered realistically then it's 3d and has shadows and just generally adds a lot of noise. Also if it isn't animated it looks shit. If it is then it either will snap or I will have to add lag to the shot taking.
Sensitivity is tricky, due to the nature of the controls I need to have the height of the table being the maximum power (otherwise you couldn't play full power shots vertically). Thus it's a matter of me finding a curve between 0 power and full power across that range, I've hopefully made a decent effort at balancing that.
The back button on the device should do whatever the onscreen back button does.
Can you point out a place where it doesn't?
Ad space, if the drag starts inside the table, the ad space should become dragable. (A little bit of padding between the tale and the edge of the screen wouldn't be a bad idea either.
Good point, I'll look into this. Of course the ad-free version won't have this problem

.
edit: Sorry, not possible at least in my framework. I don't get touch events in the adview.
I'm just now trying out the challenges, there should be a prompt in the center of the screen after you fail or complete a challenge.
I had this in at one point and wasn't happy with it, it was just repeating information that was already on the screen and looked messy. Probably my implementation but I'm afraid that's all that's possible!
I don't think it's needed but I'm always annoyed there's no easy "exit game" function, you always have to drill back to the main menu to exit it properly.
Yeah not sure about that one, once you're out of a game (which is difficult on purpose) you can just hammer the back button. That also doesn't really fit with Android's ideas, you can use the home button to leave the game no problem.
Thanks again.