I've just finished Tales of the Ketty Jay and it turned out to be a great popcorn steampunk/fantasy series
The steampunk airship aesthetic, coupled with a cast of likable characters and a fast-paced narrative, made this series much better than I initially expected. Having watched an old anime called Last Exile as a kid helped me envision action scenes in great detail, making the already cinematic descriptions feel as vivid as watching an actual movie. I think I've never read anything as fast-paced before, though I'm not really much of a reader when it comes to fiction.
Another good thing about the series is that it's only four books long and the story has a very satisfying conclusion (I usually get intimidated by most fantasy series as they tend to have like 15 books anywhere from 500 to 1k+ pages each).
Daemonism is an interesting equivalent to "magic systems" that people usually expect from fantasy novels, though it's relatively restrained and grounded. There's also a group of badass characters called Century Knights that are so OP, you can't help but think the author drew some inspiration from anime or manga.
The main cast of lovable rogues has a great dynamic, often resulting in hilarious banter or cheesy exchanges during combat. The characters are mostly great, especially Frey, Jez, Crake, Malverly, and Harkins. Even the vicious cat! The only character I disliked was Trinica, she was really annoying in book two, but even then she redeems herself in the third, and to an extent fourth, book. Characters grow significantly starting from book two, and Frey in particular grows from a complete asshole into a likable leader.
Have I mentioned that action sequences are breathtaking? I particularly like those from the first and third books, especially the ones involving Harkins. If you're into steampunk, swashbuckling, and aviation, the series is an absolute treat.
I think that comparisons to Firefly are going too far though, there are few similarities other than the surface level "a group of smugglers living and traveling together on a ship". I actually dislike Firefly and think that only the pilot episode was good.