I noticed a lot of complaints dealt with the finicky and fussy nature of the Celestial Brush as used by the wiimote motion control. I too had some problems getting it to do the right things and I have had frustrating bouts of repeating a timing-based minigame, but I think I have a technique that can reduce the problems.
The game still is a little picky about where you've placed your strokes and your timing, but I've found a trick to moving the wiimote when painting: don't move from your wrist. Instead, move your entire forearm as a single unit and keep the wiimote pointed straight-on (perpendicular) to the sensor bar. Move from the elbow and shoulder and you'll have a lot better luck with your brushstrokes. (This is, incidentally, how one moves the brush when painting in most traditional Asian painting styles, to lock the wrist and move the entire forearm.) Furthermore, don't extend your arm out towards the TV, but keep your elbow in close to your torso.
The tying-vines-to-log-going-over-waterfall minigame almost stymied me. Then I found this was the way to hold and move the brush and it became a snap, and I was able to move on with the game.