Actual rules changes in Iyanden supplement?

For my army background I am planning on having an Archon that subverts/breaks a Spiritseer and forces him to bring the dead Eldar to assist him in his raids.  It would be Dark Eldar Primary with Eldar wraith allies.  The Iyanden supplement seemed perfect for this but my local store does not have a copy in stock.  Before I order one I just wanted to know if it is worth getting.  I know it has lots of history, fluff, and pretty pictures along with a rule allowing a Wraithlord/knight to be the Warlord.  Is there any other rules in the codex that would make it worth purchasing for my idea?  My warlord is going to be my Archon so the only rule that I know is in the book does not apply to my situation.  If the book will not be useful I would much rather spend the money on another box of wraithguard instead.  Thanks for any input.

There's a few things in there yes, different artefact list, different warlord traits, spiritseer equivalent to the warlock council, special psychic power that boosts the wraiths and 3 new missions, plus cities of death and planetstrike stuff.

It's an expencive book but I have liked playing with it. The Shadow Council has been and will be a big thing in my lists.

Thanks for the replies. The artifact list and new psychic powers may be worth it. I will look into it. Thanks again.

The Iyanden book is awesome. I bought it as soon as it came out and have played it every game of 7th edition. It has the best warlord traits of any of the codices, the artifacts are fantastic, fairly inexpensive and very useful (The Soulshrive is what the huskblade should be and has reaped untold glory for me in every game) the Shadow Council is great and there are TONS of awesome missions, Eldar expansions for city of death (ever wondered what Eldar landmines did?) and best of all its completely interchangeable with stuff from Codex Eldar. Not to menton that I was surprisingly entertained by the fluff.... if you ever wanted to know about Prince Y'riel you pretty much get a run down of every campaign the Admiral Prince of Iyanden has ever fought in. Very cool stuff.

Just a forewarning, there is only literally 2 pages of rules for the army supplement. The rest is fluff and Altar of War mission(s), but I would still say the book is totally worth the price. It has a lot of great back ground fluff and what not.