I'm not going to lie, I did enjoy Skyrim quite a lot when my friend lend it to me a couple of years ago. The game has a lot of detail and content that the game, at least to me, felt never ending. That said, it's quite difficult to compare two different genres of games that have view similarities. In fact, I still remember the whole "Skyrim vs Skyward Sword" argument which lasted longer than it should have and was only started simply because the two games had the word "sky" in their names. Content wise, Skyrim has the upper edge compared to Zelda. That said I think if it wasn't for Zelda, Skyrim wouldn't have existed simply because in terms of an open-world, Zelda did this first since the very first Zelda game. Not to mention Zelda just has that charm and replay value that always makes me return to play for me even when I finish the game where as with Skyrim once you did everything the game offers, there's really nothing better to do than just roam around the map or delete your file and start anew at least from my viewpoint. Perhaps Skyrim is better than the handheld Zelda games, but the 3D Zelda will usually if not always have the advantage compared to Skyrim. Zelda just has that special mix between adventure, plot, and everything between that not many video games have so if I were to judge the two series, Zelda and Elder Scrolls, very critically I would personally would pick Zelda for its charm and replay value.
Simply because the Wii U is more powerful compared to the Xbox 360 and the PlayStation 3, I do believe that an open-world combined with non-linearity will give Zelda U the advantage compared to Skyrim. The technology by comparison has improved so it would make sense that Zelda U will do better than Skyrim, but it's too early to answer that question and thus we have to wait until more information about the game is revealed.
I posted this earlier, but Zelda isn't the first open world game. It was certainly extremely influential but it wasn't the first. And even if it was, someone would have done an open world game eventually imo.