I'm not an advocate of touchscreen gaming, but there aren't that many buttons... are there?
Tools: Swipe to open, tap to select.
Paint: Swipe to open, tap or slide to select.
Bricks: Swipe to open, tap to select w/ another button to open the menu.
Place Brick: Tap on screen with brick panel open to place a ghost brick there.
Rotate Brick: Tap on the ghost brick.
Fire: Tap (or hold) the screen while the tool menu is open.
Painting: Hold the screen while the paint menu is open.
Activate: Tap with no menus open.
Look: Gyroscope (toggleable) or sliding the screen.
Jump: Tap with two fingers.
Jet: Hold with two fingers.
Light: Button in the lower left.
Zoom: Pinch or expand fingers.
Crouch: Button in the lower right.
Menu: Button in the upper left, contains more features than the PC one because they can't be all fit into touch controls.
View: Toggles first/third-person, upper right.
Overall, it's not too bad, but it's still not worth it unless someone makes an add-on.