I think that, naturally, Twilight Princess was very similar to Ocarina of Time, just as Super Metroid was very similar to the original Metroid. In other words, you can't possibly expect a central idea, especially one which acts as a core to a series, to be elaborated upon without such an elaboration borrowing elements from that central idea.
Beyond that, however, what exactly did Twilight Princess borrow from OoT? Certainly, the locations, but what did, say, Karkariko, or even Castle Town, have in common with their N64 counterparts? What traits, other than appearance, did the Zelda of Twilight Princess (who is solemn, reserved, and wise) really, deeply share with the Zelda of OoT (who was filled with regret, open, and personal)? What did Link's motivation in Twilight Princess (to save his friends, and eventually his kingdom, from a foreign threat) have to do with Link's motivation in Ocarina of Time (to experience the world by setting off blindly on some fool's quest)? Or the dungeons? Twilight Princess' Dungeons were large, winding, and intensely thematic; Ocarina of Time's were dense, trial-based, and only mildly thematic. Even the set of characters differed from one another: Twilight Princess' were individual, independent, yet products, of the world around them; Ocarina of Time's were very much elements of the world in themselves, crafting the environment around Link.
These, of course, are very few examples of the many differences between the two titles.
In terms of evolving the franchise, revolutions don't come in the form of new structures or game-play mechanics with a ribbon smacked on top. While OoT's additions were extraordinary, Twilight Princess worked wonders with the cinematic structure and presentation of the series (which, admittedly,has since been fractured with the release of Skyward Sword).
Overall, Twilight Princess was an epitome of subtlety, while Ocarina of Time used more immediate means to accomplish its goals. People who don't recognize these subtleties tend to relate Twilight Princess heavily to Ocarina of Time because the N64 title is familiar to them. Beneath the surface, beneath the locations and the lore, Twilight Princess is an installment to the Zelda franchise that is astoundingly unique in its ways, yet so very cheated because it happens to be the first Zelda title since Ocarina of Time featuring a fully explore-able, 3d Hyrule.