j-r conlinTold to me by a UX person who I deeply admired:
New is not better.
Better is better.
Working with something a long time doesn't make it better, it makes it comfortable.
It's easy to confuse comfortable with better.
It's easy to confuse new with comfortable, particularly if you're the one making the new and have gotten comfortable with it.
It's critical to give the new thing to someone comfortable with the old, as well as new to it all and see if they think it's better than what they did before.