I love this port of gubble, but a problem is that the controls aren't so good. You might want to consider making it so you can choose between the current style, joystick, and arrows (one version is putting the arrows on the left, right, top and bottom of the screen, and the other is just a mini one, and you should be able to decide where to put the mini one and the joystick). Also, you should be able to choose where the float button is, not only from the places in options. Also, you should be able to choose its position on the screen. (sorry if I'm being picky, but I'm just trying to help make it better). If you did some updating and advertising, this would definitely make one of the top few apps.
When you're go on a spring with a tool and hold the hover button, the tool is in midair, making it unaccessible.
Also, where are all the blockades in the original game?
A suggestion (you don't have to take it, just think about it) is that you have to unlock the minigames.
A glitch-ish thing: when you're hovering above two tools, Hubble goes crazy.
Another one is the world names (instead of just world#) and maybe the so spinning before a level (and the option to turn it off).
And once you've pretty much made it perfect, you can add a level builder.
But overall it's a good port, almost identical to the pc one (except for the blockades).
This would definitely make the top apps with more advertising.