The optical quality is very good, but the lens does have a drawback: the focus ring and front element rotate during auto-focus. This makes using a circular polarizing filter less convenient. And you have to learn to avoid touching the focus ring!
I wanted the telephoto zoom for wildlife and landscape photography. With this lens and the 17-85mm kit lens, I’m covered from 17-300mm (27-480mm equivalent for 35mm film).
I don’t have a fish-eye lens, and the wide angle end of my kit lens is not great, but I’m not much into wide angle anyway.