I thought it was fun if you don't take it too seriously.
There was a scene where Supergirl was flying slowly through some trees and it was clearly Helen Slater in a harness. I was so mesmerized that words could not have described it. It was a majestic scene in many ways.
There are people who say the one thing the Superman movies got right was casting Chris Reeve as Superman. I would say that, if they did nothing else right, they cast Helen Slater as Supergirl. She almost singlehandedly makes the movie worth watching.