Okami is a fantastic game, but if at all possible you should play the PS2 version. The Wii version was not ported by Clover themselves, who I believe actually went bankrupt. The group who took it up and ported it did a fairly sub-par job adapting it to the Wiimote. Namely, combat is a real chore with any weapon other than the Rosary Beads, with attack combos being impossible to pull off consistently.
However, the Wii version of Okami is only badly done compared to the PS2 port. Compared to games in general, and most of the Wii's library specifically, it is a real gem, right up there with Mario Galaxy. I'm not saying "don't buy the Wii version of Okami", I'm saying "Get Okami, you won't regret it, but if possible get the PS2 version."