If you're going to be using it for a 3.5 game and are already very familiar/comfortable with the Eberron setting, I'd give it a miss.
The main selling points, IMO, are:
1) Great overview of the setting and the main themes (the first chapter).
2) Good overview of the 3 main "world-spanning" opponent organisations (Aurum, The Chamber, Lords of Dust).
3) Much more logically laid out and inclusive geographical overview (chapters for Sharn, the Five Nations, Greater Khorvaire, and the rest of Eberron, each broken down into one or more double page spreads for each nation/area).
4) Very comprehensive knowledge check (4e specific but fairly portable to 3.5) tables for information about each nation/organisation/area, i.e.: history, geography, religion, etc, tables for each region with increasing information based on how high you roll (much like the 3.5 Players Guide to Eberron).
5) Good overview chapter of the various dragonmarked houses (double page spreads for each), including "house" Tarkanan.
6) Excellent interior maps & poster map. Not only the best I've seen for Eberron, but probably the best I've seen for any D&D campaign setting. Of course, tastes in style are very subjective, so check out the previews on the WotC site to see if they're your thing.
7) Integration of 4e races & cosmology (probably not of much value to you if you're only playing 3.5).
So I'd highly recommend it. As someone else said, if I was choosing between the 3.5 or 4e versions, I'd definitely recommend the 4e version. I also wouldn't hesitate to recommend it to someone who owns the 3.5 version and is planning on running 4e (as an aside, I'd also highly recommend 4e for running Eberron - the fast and loose, high action, low realism nature of 4e lends itself very well to the style of Eberron).
However, as I said right up front, if you're determined to run Eberron using 3.5 and you're already very comfortable/familiar with Eberron, you probably won't get a lot of value out of it...