I received my copy of Eberron Monday before lastand have been reading it most of my spare time since. It is quite a lot to take in.
In my opinion, Eberron is DnD all growed up.
I have been playing in many different campaigns since 1978. Eberron really appeals to my mature(?) style of DnD. I guess I should qualify my above statement in that there are roleplaying games other than DnD directed at a more grown up audience. There is always going to be an element in a game that is unique to DnD, and I think Eberron hangs onto it and presents it in a newer light.
Is it the best? Maybe not. Does it work in a new and interesting way? I really think so. That is why I find it interesting that it doesn't interest accomplished and knowlegable DnDers like Buttercup and others above in this thread.
My real concern is the complexity. I can see newbie DMs with grey matter leaking from their ears trying to take this in. An experienced DM, comfortable with the 3.5 system, would have little trouble indoctrinating any group of players, regardless of experience, into Eberron. A new DM, trying to learn the basics AND Eberron's complexities, would be lost.
I recommend that new DMs try to gin their thoughts on this setting down to about one page of summary to get their bearings. If they choose to use Eberron, don't try to introduce it all at once.
I think this setting will inspire some great play. I hope others give it more than a passing look.