Fallout 3 had a far more interesting world than Oblivion or Skyrim, but it still managed to get repetitive before too long. While we had some interesting places such as Tenpenny Tower, Vault 108, Rivet City, and Andale, the majority of the world blended together after some time save a few exceptions. Again, this was a problem New Vegas addressed with more varied and distinct locales such as the Big M.T. facility, Novac, Jacobstown, and New Vegas itself among others.
The problem is Bethesda’s worlds are usually so large, they get repetitive quickly. So why not make a smaller, more interesting game world with more depth and variety? Or do what Obsidian did and just populate the large world with more interesting places? Bethesda can make some interesting places to explore, so why not focus on making a better world instead of a bigger one? Bigger is not always better. Also, more snow! Don't you want to build a snowman?