People relate to a certain level of expertise. That’s no secret; it’s part of how we choose doctors, elect presidents, root for sports teams. It’s also a good part of what readers like in their protagonists and support characters. It gives them something to admire while also–especially in the case of the protagonist–being a bit of wish fulfillment.
There’s no shortage of examples of this done well: Harry Potter’s excellence at Quidditch; Katniss Everdeen’s marksmanship with a bow and arrow; Sherlock Holmes’s genius. It would be easy for them to become obnoxious if their skills were allowed to dominate the story, but the writers manage to avoid those pitfalls.
What makes them work is that they each have narrative tricks that keep them human. Harry is prone to making rash decisions, often with disastrous consequences. Katniss’s devotion to her little sister strikes a chord with the reader and establishes sympathy. Sherlock’s stories aren’t told from his point of view but from Watson’s, so we get to see his difficulty relating to people and his struggles with addiction from an outside perspective.
Without that humanizing influence, you end up with a character like Kvothe from The Name of the Wind. Now, the book had other things going for it; I loved the setting, the feel of history that Rothfuss brought to the text, among other things. But I couldn’t for the life of me relate to Kvothe. To me, there was no softness to him, no moment of sympathy. The whole story was a list of all the incredible things he’d done and reasons he’s the best at anything he turns his mind to.
Which, I suppose, works for other readers. For my money, though, I like my genius with just a twist of humanity.