Summary — A well-produced, refreshingly small-scale superhero movie, but uncreative action and a forced take on Supergirl's personality kept it from being much fun for me.
The production was good and it has that classic Hollywood superhero-movie polish. I actually liked that it didn't try to be bigger than it was. The story is basically about saving a dog rather than saving the world or the universe, and that smaller scale was refreshing.
The action scenes clearly had a lot of production behind them, but they weren't especially creative. Supergirl herself also felt like the movie was trying too hard to force her into a specific personality trope. It wanted her to have this party-girl thing going on, but without really letting her make the kinds of mistakes that would come with that or capturing any of the nuance that could make it interesting.
There was also a character named Merrick — the first Merrick I've seen in a blockbuster movie — and of course they were evil. They tricked Supergirl and tried to sell her to slave traders.