Alita is enjoyable in the turn-your-brain-off-and-watch-cyborgs-beat-up-other-cyborgs kind of way. If you go in expecting that, I think you'll enjoy yourself.
Serenity...I still don't know what to think about that thing. They even stopped promoting it because the test screenings were so bad. That's pretty bad when the movie bails on itself.
And I hadn't really given TKWWBK much thought. It seemed like a generic kids movie from the trailers, but seems like it's more enjoyable from what you said.