I think the first three books are all so amazing and they made me cry and I struggle to rank them they're all amazing in their own very different ways.
The fourth book was fun but definitely the weakest of the series and didn't feel like a very fitting end. I think it suffered from the same issues most 2020-Inspired works do of clearly pulling too obviously from the events of 2020 but then having an easy end to whatever emergency is standing in for COVID. So now in 2022 the story has immediately aged poorly as a quaint thin Quarantine story that ends with everyone just getting to put it all behind them and go back to normal, which simply isn't what has happened in real life. Maybe in ten years it'll be easier to feel something when reading some of the scenes that clearly are referencing experiences from 2020 that were held by people not classified as essential workers. The characters were likable but none as deeply compelling as the earlier books. It was fun and I enjoyed it but it didn't feel like a series finale. I think I'd say Wayfarers feels more like a trilogy that ends with Record of a Spaceborn Few and has a Bonus Book you can read for fun that isn't a part of the main trilogy.
Gosh though this series is good how is Becky Chambers so good at writing damn