@Steampunk
Steampunk is, in my humble opinion, clearly an aesthetic. It's funky, clunky tech that does fantastical things. I think lightning rails, just like fantastic airships, are right in steampunk's wheelhouse. This is regardless of whether they are powered by steam. Like, I think relatively little steampunk is actually steam-powered. Jules Verne is one of the spiritual fathers of steampunk, and I think the Nautilus is nuclear-powered. Maybe it's electric? I'm almost positive it's not steam. Escaflowne is another example -- steampunk mecha -- although I think they are powered by dragon-based phlebotinum rather than steam. But, they have the kind of retro, weird lack of tech that evokes the aeshetic.
Likewise, lightning rails are pretty iconically steampunk, whatever their pseudo-explanation.
Whatever it is, I find Eberron a little too much of a hybrid in this way. I appreciate its pulp sensibility. But, I'd appreciate it if they better calibrated the tone. I think it would make it more appealing, at least to those people who will find it appealing, and a bit more different from the standard D&D fare.
This is actually my biggest issue w/ 4E settings. By trying to make everything mechanically identical (even though they introduce 50 new powers, feats, etc. in every issue of Dragon ...), they have ended up whitewashing all the settings to make them feel too similar.
I prefer many elements of the Iron Kingdoms to Eberron, but I find it too over the top and childishly grimdark for my tastes (and this is setting aside its awful rules).
I do like the astrological take on the planes. I actually stole that for one of my games.