If you spend a lot of time complaining about "waggle" and don't like moving anything other than your thumbs when you play, then stick with the PS2. Okami is simply another in a long list of games that are fail on the Wii.
If you like the IR pointer (which is my favorite part of the Wii) and don't mind shaking the controller during fights (which I am used to form ZTP and SMG), then Okami is a must have. ZTP has better dungeons, but Okami has a better overworld and the art direction is amazing. It's like what ZWW was trying to do with cel shading but didn't quite do.
As long as you use Z for slash (which is automatic), the rest of the strokes just require repetitive practice. I think Ready At Dawn required a little more precision in the Wii version than the PS2 version since it is easier to make the strokes with the pointer, but the game would be too easy if it were really forgiving. I'm somewhere around 80% successful with the strokes the first time, and 95% the second time. It just takes practice (which reflects the practice you need with calligraphy to acheive the precision that separates good from bad). After my first dojo training session, I started reeling off 8 hit combos easily. You just have to shake the remote in rhythm. Of course, if you inclined to pounce on any shortcoming to consider the Wii as fail, then Okami does suck for the Wii.