Boring?? If it's "The Train Job" that you saw, you should be ashamed of yourself! That's a damn good episode, in my not-at-all-humble opinion.
Five main differences between 'Firefly' and 'Buffy the Vampire Slayer':
1. Quite a bit less hand-to-hand fight scenes or fight scenes in general.
2. A hell of a lot less mushy, agonizingly trite "unattainable love" angst, and the few times it does happen, it passes very quickly.
3. The show is mostly about committed grown-ups, not confused children (although there are a few of those).
4. The dialogue, while still full of Whedonisms, is very different, as it's a mixture of antiquated, futuristic and occasionally Chinese language.
5. Obviously, it's a sci-fi Western, not a horror series.
Watch, and be grateful, dammit.