The most common traits in other humans that tend to impress me: common sense, intuitive intelligence, perceptiveness, quick thinking, compassion, selflessness, self awareness, integrity.
Nature regularly and never fails to impress me, I couldn't possibly list all of the things... anything from immense mountain ranges, waterfalls, old growth trees, watching animals of all kinds work/hunt together, lightning and thunder and other awesome displays of the weather. A great many things.