Skyward Sword is less arduous than it is tedious to play. The gameplay is fairly simplistic (deciding which way to swing a sword via the Wiimote), and because of that it may seem repetitious in its own regards; button movesets arguably offer more diversity in terms of control. Additionally, I've always found "button-mashing" to be more reliable since I know that holding down A or B will activate a Spin Attack, whereas swinging the Wiimote more often than not just did a normal attack (whenever I wanted it to do a Spin Attack).
But the true source of SS's mediocrity lies outside of the controls--rather, it exists in and permeates throughout the missions. Normally Nintendo loves doing things in three in Zelda, yet in SS they took that a step farther than they should have, and instead made it a linear, coercive cycle. Starting off from Skyloft, the hub world, Link would fly to one of the three provinces below and complete his assignment, then return in selfsame fashion. That was...pretty much all of the game. Now, let's take that example and apply it to a whole playthrough. You'd have mandatory undertakings such as fighting The Imprisoned (between three to six times), dueling the pirate robots (twice and in the same enclosed space), battling Ghirahim (two repeat battles, one epic fight), and the Silent Realms (three below, one on Skyloft).
That's not counting the various fetchquests strewn throughout the game, such as collecting the windmill gear or getting the "hot tub" from Faron. Another worthy mention is Instructor Owlin's obligatory tutelage on the Air Charge, which should have been introduced at the beginning alongside more enemies in the Sky, and not shoehorned in halfway into the game.
Skyward Sword was a test run, of sorts, designed to try a lot of things out and find out how much the fans would enjoy/dislike it. While it wasn't overly difficult save for a few areas, it mainly suffered from the aforementioned desperate attempts at lengthening the game, and was committed in a very repetitive manner at that. The Imprisoned battles were especially taxing on me, and I really wish that they were implemented without a time limit (what other Zelda boss involves a time limit?) because at times it took me over an hour to progress. Nobody should be troubled with a "race to the top" scenario which automatically equates to the end of the world, let alone three times.
The usual enemies weren't a bother to me, with the exception of the Lizalfos; getting the pattern down was a lot harder than I preconceived and even then it was a matter of the utmost precision.