The best way to describe Twilight Princess is that it's another Zelda. Sure, it's bigger. It's nicer looking. And it even has motion sensing Wii controls. But when it all comes down to it, it's just another Zelda. A Zelda that got delayed a full year.
So what did Nintendo do during their crippling delays? Obviously they didn't innovate on story. While any die-hard Zelda fanboy will tell you that story has never been the focus of Zeldas past, that's not really an excuse for regurgitating the same story over and over. It's like Nintendo's playing mad libs, and I'll elaborate on that in a second. But the reason why the story is so stagnant now is because Nintendo wants Link to be completely pure of heart. They want him to be fighting only for what is good, and pure, and righteous. And pure. But Link himself has no true motivation for saving the world. He never has. He does because he can. The story would be so much better, so much more compelling and powerful, if Link found a reason to be a little selfish.
They didn't at all change their established "Zelda formula" for dungeons, and not because "it ain't broke." Solve some puzzles, get stuck, earn a new item, solve some item-specific puzzles, fight a boss, repeat. It's very repetitive and will get downright boring at times. You'll simply roll your eyes, sigh, and grind through. And the first few tutorial hours of the game? Almost put me to sleep. Literally.
To make matters just that much worse, you'll fight in the same dungeons you've been fighting in for 20 years: Forest, Fire, Water, Sand, Shadow, Hyrule Castle, etc. You even fight Queen Gohma from Ocarina of Time again. Oh, and by the way- all of those are horizontally flipped from the GameCube version of Twilight Princess because no one wants to upset Zelda fanboys by making Link right-handed for one game.
Now, about those mad libs. Nintendo just went through and swapped things from past Zeldas- A Link To The Past let Link transform into a pink bunny, Ocarina of Time let him transform into a child, and Twilight Princess lets him transform into a wolf. Ocarina had Navi floating around, annoying you with tips you didn't need or want; now you've got Midna, who somehow lives in your shadow. (On that, it doesn't make sense that Link's regular shadow disappears when talking to Midna. He's still blocking light; he should still create a shadow. It's just logic.) A Link To The Past had the light and dark worlds, Ocarina had child and adult, Minish Cap had big and small, and now you've got the light and twilight worlds.
Let's talk about the Wii controls for a moment. Here's the pros: You don't have to charge your spin attack, it's a hell of a lot easier to aim projectiles, and the novelty of motion controls last for a little while. But the cons outweigh the pros: Using the remote for sword swinging/wolf biting is imprecise and eventually devolves into rapidly shaking your wrist like you've got Parkinson's, the camera is more fickle, the novelty wears off fast, and then there's Navi.
I'm going to devote an entire paragraph to Navi. She was your fairy in Ocarina who hovered above you, and now, despite the fact that she serves absolutely no purpose, she's back and somehow more annoying than ever. There's no use for it, but Navi will let you know where you're pointing, and throughout this ~60 hour game, as you move the Wii remote (a lot), she makes an irritating twinkling noise. So why is she there; what purpose does she serve? No reason, no purpose.
Once you've spent a good portion of your life adventuring as Link, as with all Zeldas, you never get to see your effect on the world. There's just no reward for it all. You save the world from evil and shadow and corruption, risking life and limb, traveling to the far corners of the world, and once you finish it just reverts back before the last dungeon. It's like a cruel joke. I just want to see the world of Hyrule in all it's former splendor; isn't that what I was fighting for?
The graphics range from amazing to ugly (occasionally the light bloom is so fierce that you won't be able to see Link's face), the music and sound effects are mostly recycled from past Zeldas (some of the new stuff is great though), and the level design will only "wow!" you if you've never played a 3D Zelda before. One of the worst things about the game, about almost all Nintendo games, is that there's no voice acting. So between further eye rolls, you'll be lazily clicking through dialogue box after dialogue box, and none of it is the least bit interesting. Not to mention that there's little to no replay value, so if you bought Twilight Princess, by the end you'll wish you'd just rented it.
That's not to say that the game is a complete failure. It isn't. If you've never played a 3D Zelda before, you'll find the game epic, refreshing, and very, very fun. But if you have, you'll know that being "another Zelda" isn't the worst thing in the world; half the time you'll genuinely be having fun, and the other half you'll be wishing that Nintendo could've done more with that extra year they took.