I've found that using the accelerometer controls works better for me, though even that takes some getting used to. The virtual stick controls are indeed very difficult to control Sonic.
Just tried it on my friend's pb, it's a good port in regards to the sounds and graphics, but as others have said it is very difficult to use the control pad. I find most platformers awkward at best on a touch screen but the controls on this one are exceptionally hard to use.