Usually I find that when a game starts out bad, it gets better as it goes on. In this case it started wonderfully. By the time I got to the volcano region, frustration and tedium alternated one after another. I wouldn't say Skyward Sword is the worst in the series, but it's definitely the worst of the 3D titles.
The best aspect of the game is the motion controls. The satisfaction of slaying a monster with your own hands really puts you into the game. Many of the monsters now have their own clever way of taking them down, instead of just wildly swinging your sword. Many enemies are challenging, as my main complaint about past 3D titles was that enemies were too easy to fight. On the negative side of the controls, the shield-counter mechanism is interesting for reflecting projectiles, but it turns some fights into simply standing there, waiting for the right moment and countering. The Beetle and the item upgrading are great additions to the series. You'll also spend much of your time having to recalibrate your controls, a task made easier when you can center the pointer on certain screens.
Stages and dungeons are rather small and linear. You'll spend much of your time making shortcuts along the way, and for good reason. This game adores finding ways to make you return to the same areas for fetch quests and an escort mission, even through the first dungeon again. The dungeons themselves tend to only have six to eight rooms, rather puny compared to previous Zelda titles. The world above the clouds is also rather uninspired compared to the Great Sea of Wind Waker, with only a few actual buildings among the tiny chunks of rock where you'll find Goddess Chests. The slowness of piloting the bird made me not even wanna bother collecting those.
Then there's Fi, who forces herself into your face frequently. There is an 80% chance that she will do so for the lone purpose of reiterating what an NPC just said seconds ago. She will also pop up to tell you where you need to go next, even if you've had to perform this same action twice already. Her text also rolls by slowly, leading many frustrated gamers holding down A, doing what little they can to speed it up.
All in all Skyward Sword puts controls innovation first, and level design second. I feel it should have been the other way around.