One more thing about panels. You have panels docked to right side. Then rotate device to vertical, then again to horizontal. And your panels would be docked not to the right side, but somewhere closer to the center. It would be good to have memorizable placement for horizontal/vertical ipad orientation.
And one more thing about brush modes: ellipse and rectangle. Angle of it is pinned to canvas orientation. So it is impossible to draw ellipse in one step. You have to draw ellipse in new layer, then transform/rotate ellipse to needed angle, then merge layers. To complicated. Why not rotate canvas and draw ellipse with needed angle in one iteration. Maybe this paragraph would be obsolete after quick shapes added.