I agree with most of the other comments so far, the "magic" of the show is going to be hard to replicate.
My bull case for this is that Nathan Fillion and crew have had 20 years of exposure to this fact and likely know what they're getting into and how to do it right. The only question is if they'll be able to execute. I'm excited!
Say what you will about Joss Whedon, but his use of a colorful character palette & quirky, punchy style of dialog have gone from niche to mainstream in the 30+ years since Buffy. Mostly thanks to Whedon’s and his imitators’ escalating success with that formula: The Avengers, for example, took Marvel from a series of above-average superhero hits to total cultural dominance.
There’s plenty of writing talent out there that grew up wanting to emulate Buffy and Firefly, so if hearts and budgets are in the right place, recapturing that part of the show should be eminently feasible.