First I would say this is possibly the worst edited book I have ever seen from WotC. And it is not just in the editing, just the way many of the paragraphs are written seems "wrong". Remember back a few months when WotC website had a series of articles on how to write feats and such, I think this books violates every rule presented there.
Once you get past the editing then there is the recycling. A lot of material here comes from Dragon Magazine and the "Races of" series. I added the Tallaire back when they first appeared in Dragon, it is a little late to bring them to me now. And I did notice that they did not recycle any psionic content from the Eberron or Forgotten Realms books, are they off limits?
Then there is the Errata, I should not have to pay for errata, that should be made available at their website. And considering the reaction to the Astral Construct errata, hopefully it will be errataed once more.
OK, now that I am past that, what about the content?
I really like the classes! I do not see the Ardent as a psionic cleric, I see him as a theme-caster, like a sorcerer with all fire spells. The key difference is that they get to add additional themes as they advance. It would be very interesting to play an Ardent from 1st to 20th level. I doubt I could guess what Mantles I would actually choose because the path of the adventures would be the deciding factor.
The Divine Mind is good, but it seems lacking on the Divine side. Maybe if the mixed a Mantle with a Domain? I do like the Lurk, especially the fact that he gets ALL Lurk Augments and doesn't have to pick and choose from a feat list.
And yes, when you combine these with the Psion, Wilder, Psychic Warrior and Soulknife from the XPH, the Psychic Rogue from the Mind's Eye and maybe the Akashic from Arcana Unearthed, we can have an all Psionic Party.
The prestige class section is a waste of space. It is not just that there are so few, it is also that they are so class specific. The only one that applies to any psionic class is the Flayerspawn Psychic and it is destined to be an NPC class in most campaigns. And yes, I agree that this new format is too wasteful, I have used several of these new format PrCs, but did not use any of the background because it did not fit my setting.
There are many very good feats, but far too many are Racial feats (including the Host & Illithid feats). There are many new powers, but far too many are Mantle only and there are a few Psionic items and Monsters, but they are "meh".
I also agree the Elemental Stewards don't fit. Maybe there was an elemental prestige class that was cut or something, but they should have been replaced with some "Host" creatures other than Quorri so that the Host feats can be used out of Eberron.
Overall the book does add several new ideas to Psionics and provides several new options, but it is a fixer-up'er, be prepared to have a lot of editing mistakes to correct and more than a few DM descions to make on what to Rule 0 and what to expand to all Psions