It's no secret that Nintendo loves to reuse old ideas in their games. If something works, they aren't going to change it. The Zelda series is a prime example of this.
The 3-D Zelda games have basically stayed the same since their first one, Ocarina of Time (with the exception of Majora's Mask). Twilight Princess continues this trend.
The game has top-notch production values, as with everything Nintendo does. The music is, as always, incredible. There are some moments of pure beauty on the soundtrack. The game looks amazing for a Gamecube game, and I think this is down to its art style. It's not as stylized as Wind Waker (which I think will hold up better in the future), but no one can fault this game for being bland. It definitely has an art style to call its own, drawing heavily from OoT but still having its own identity.
The story is a mixed bag for me. It's presented very well, something that the art style helps a lot with. The story itself is kind of bland, however, and you don't really meet any interesting or colorful characters (with a few exceptions, of course). People have said that the game has a dark story, but I don't think it's particularly darker than most of the other Zelda games. I think it seems that way because of the graphics and how well the game is presented. If you're looking for dark Zelda, however, Majora's Mask still takes the cake.
However, the gameplay is what will make or break the game, and in this case, it's classic OoT-style Zelda. The formula is pretty much exactly the same: get three things, something happens, get more things. The dungeons are pretty much the same too: get halfway through the dungeon, get an item and use it to solve the rest of the dungeon. Unfortunately, this makes the game predictable. In some cases, you'll get an item in a dungeon to never use it in any other parts of the games (i.e. the Spinner), which seems like a missed opportunity.
The overworld leaves much to be desired as well. It feels strangely empty; somehow WInd Waker, which was much, much bigger, felt fuller as well. There's secrets hidden in the countryside, but usually just an expansion for your inventory or a heart piece. Throughout the game, the overworld never really entices you to search for its secrets. It's just the place in between all the other places.
Overall, this game is basically Ocarina of Time 2.0. It doesn't deviate a lot from the formula that that game used, so if you're sick of Zelda, this game won't change your mind. If you're still craving some more OoT-style Zelda, though, this game might just scratch that itch for you.