A walk in the park is nice, but it’s exceptionally nice on a beautiful spring day when the weather is perfect, flowers are blooming, and birds are singing.
Think of the word exceptionally as a magic wand that upgrades adjectives from ordinary to extraordinary. For example, a good day could just be a pleasant day when nothing bad happens, but an exceptionally good day would be closer to having the best day of your life. While exceptionally usually carries a positive meaning, it can also be used to describe something that is particularly unusual, like an exceptionally large shrimp.