I'm writing this reply without having read the thread!
The reason that I like Eberron is pretty simple. It takes the familiar elements of Dungeons & Dragons and puts them in a non-traditional context which is more in line with contemporary trends in and attitudes towards the fantasy genre.
The politics of the setting, for instance, are much closer to those of Europe after the First World War than they are to those of the standard quasi-medieval fantasy setting. There are agitators for democratic rule in the most progressive kingdom, for instance, and an entire culture of dispossessed refugees who can never return to their annihilated homeland.
The races of the setting take the most basic traits as described in the rules and use them in a completely different way - elves, for instance, are not nature-loving forest-dwelling Übermenschen, but they are a long-lived, magically-inclined, martially-skilled people as the rules describe them. With a few exceptions, each race exists in more than one culture, as well - to again use the elves as an example, there are jungle-dwelling elves who preserve their ancestors as deathless and look to them collectively as a gestalt deity which guides their culture, there are horse-riding warrior elves who seek to embody their ancestors' great spirits by emulating their heroic deeds and who carved themselves out a nation during the Last War by treachery and ferocity, and there are urban elves who are completely assimilated to the major nations of the continent of Khorvaire and consider themselves "Brelish" or "Aundarian" as much as they are "elves".
The magic of the setting is best described as "widespread, but not powerful". Eberron's level of "technology" is roughly equivalent to that of the real world during the Industrial Revolution, but rather than being powered by clockwork or steam, it's all powered by magic. There are airships and trains powered by bound elementals, a magical telegraph system, towers built impossibly tall because their city stands in an area metaphysically "close" to the plane of flight and the sky, and an adventuring class (the artificer) which focuses on constructing temporary and permanent magic items rather than on casting spells. For all this, though, there are few high-level characters of any stripe, including spellcasters, and the orientation of much of the most powerful magical effects is practical rather than adventurous, and requires the contribution of dozens, if not hundreds, of artificers and other spellcasters - building an airship is not the sort of thing a wizard can do in her spare time!
The other aspect of Eberron's widespread magical "technology" is that the majority of it is in the hands of the dragonmarked houses, family dynasties within the "common races" (i.e. those found in the Player's Handbook, as opposed to those native to the setting). Each dragonmark grants those who bear it certain minor magical abilities, but the real power of the dragonmarked houses lies in the way they've developed various magical items in order to enhance and amplify the power of their marks. These powers and items enable the houses to operate virtual monopolies in various areas of commerce linked to the powers of their mark, and (in the case of House Cannith, the human dynasty with the Mark of Making) has enabled them to (admittedly inadvertently) create an entire race of sentient, living constructs.
Getting back to the tone and attitude of Eberron - it's intended to be more like a fantasy version of The Maltese Falcon, or a D&D-fantasy version of the Indiana Jones films - intrigue, two-fisted action, and other pulp and noir tropes combine with the familiar ideas of heroic fantasy to provide an alternative to the traditional, pseudo-medieval Tolkienesque settings with which D&D has traditionally had the most success (the Forgotten Realms being the canonical example).
I have the feeling that Eberron will be more successful than other non-traditional settings - Planescape, Spelljammer, Dark Sun, Ravenloft - simply because, at its heart, it's still D&D the way it's always been played. You can have the same basic kinds of adventures that you have in Greyhawk or the Forgotten Realms, but with a more modern, less traditional feel and more twists and turns along the way. This means that there's at least the appearance of more variety and familiarity than there is in a setting where you're flying around space in a sailing ship, or trying to survive in a desert wasteland, or running around metaphysical worlds of belief.