I'm right at the final boss in the Wii version, so I feel that I can speak for most of the game. I haven't beaten it yet because the final boss is 13 minutes long, with no checkpoints, and the final sequence in the fight is something the game has never thrown at you.
That being said, I think that the Wii version of Rodea: The Sky Soldier is definitely worth a playthrough if you're a fan of Naka's previous work, mainly Sonic and NiGHTs. I mean, it's all there- the level design is very reminiscent of Sonic Adventure 2 though with more open areas (and plenty of alternate paths), and the flight mechanics are very solid. But it is so much a retread of those concepts that it won't surprise you very often. The sense of scale is really quite something, and the amount of levels and boss fights that are really huge is impressive, but the gameplay challenges themselves aren't mind-boggling and are often familiar.
While the first two bosses- both giant and Rodea-sized- don't do much in terms of difficulty, they are at least novel and enjoyable. However, the second half of the game really pushes the combination of giant battles and flight mechanics to the extreme, and its very satisfying. Even the Rodea-sized bosses change it up a bit, and it makes them feel unique rather than clone-like.
There's plenty to do in Rodea- collecting the massive amount of medals that are tucked away in each stage, as well as attempting to S-Rank missions in both time and gems (I find it hard to believe you can do both at the same time) contributes a great deal to the overall playtime. The battle mode is actually really rewarding because you can interfere with players as you race through the stages. If this were a game released in my childhood, I would have played the hell out of it and it would have become a favorite, for sure. But, I have already played a game very similar in design, and at that point in my life, as well, so I can say that I have enjoyed Rodea a whole lot, but it is not my favorite game. It's well-crafted and you can see a lot of effort was put into making a quality and unique Wii title, but it won't be remembered by anyone because of its limited release. That's too bad, because it is REALLY fun.