Dragons of Eberron is a nice addition to the campaign setting. In my mind, it should appeal primarily to Eberron DMs (especially those running a higher level game) and anyone eager to devour the settings lore. It contains little in the way of new monsters, feats, items, or prestige classes. While some DMs might take advantage of the numerous maps or statted out dragons, I think the book as a whole would not be very useful for the generic D&D and player.
As the title implies, if you are interested in the dragons of Eberron then the book is for you. It is well written and contains lots of useful insight and information. It covers the outlook and culture of dragons in general, the mysterious draconic continent of Argonessen, and details many dragons found in other parts of the world.
Of course, the pending release of fourth edition D&D may make some gamers understandably hesitant to buy 3.5 edition products. However, if you are planning to run Eberron in 4E I think this book could still be a valuable source of information. Of course, the stat blocks of specific dragons will probably be (more or less) obsolete but much of the book contains detailed lore and descriptions that will be useful reguardless of the rules set.
Overall I give this book a rating of 4 stars. It is well worth getting if you are interested in the subject matter and want to use dragons in your Eberron game; however it is only of limited utility to generic D&D players.