Hmmm. I like that. Tell me more....
Where to begin?
Quick overview? (Free of major spoilers)
The first module has NO dungeons. (Sure there's some locations to explore, but nothing I would qualify as a "Dungeon".) It's very "Pulp"-ish, trying to escape a City under siege.
The second? A trek through a Fire-Forest. (Tone-wise, I love this module, but I'll admit that it IS a bit of a railroad.)
The third? Really brings the intrigue in, as the PC's try to neogiatie with various factions, as a hurricane swirls all around them.
You get the idea, I think.
The benefit of "Burning Sky" is that (as Ryan said), you are truly heroic charcters, in an EPIC sense (not Epic-level-wise, but on the general scale of things.)
You know who the enemy is from the start (though there ARE some twists, needless to say), and must work out alliances to defeat the greater evil. And your actions have consequences; if you piss off the Shalahesti Elves, they're not likely to rally to your cause, for example.
I'll be using Eberron. Can I jettison the RotRL background w/o seriously harming the AP?
With Pathfinder, you COULD transport things to Eberron, but it seems like Pathfinder is much more useful in using the world they establish, as well as being part of the appeal.
So, conversion-wise, I think "Burning Sky" might be easier to manage. (For instance, most of the faiths listed are generic. [IE: Torrent, a cleric in the first Burning Sky adventure is listed as a "Water Cleric", allowing you to subsititute a deity of your choosing without impacting much.])
My thought?
Pick up both if you can afford it!
Oh. My. Uh, when does the compedium get released?
Sometime after the series is completed, I would think.
And they seem to have foundered of late; the 7th Module was released a few weeks ago, and I haven't heard about the release for the 8th and beyond.