I've mostly finished digesting the rules from a theoretical standpoint. Most everything is acceptable, but flying stuff scares me. It's going to be pretty constraining to my lists to get any kind of skyfire into my Eldar and Tau. I think it really holds that if you had a solid codex going into 6th--you're good. If you had a bad one, you didn't get many favors.
There are a few things that I want to call out that I haven't seen anyone else really mention. You can't use psychic powers the turn you deep strike. And double toughness instant death is calculated off of modified toughness now. I really think Attack Bikes>Land Speeders this edition.
While the 6th rulebook is not so bad, the Eldar FAQ was horrendous. It had to be written by an intern. They printed "sentences" instead of "paragraphs" in the update for Veil of Tears. You can interpret the rule several ways now going from abjectly useless to game breakingly awesome. You have to infer that spirit stones and Eldrad's staff give +1 mastery level. Speaking of Eldrad's staff; it's a total mess. Does it still allow you to use the same power twice? It's listed as "ignores armor saves", but is not considered a power weapon, and is not in the master appendix with an AP. So what is it? My interpretation is RAW and that it ignores ALL armor saves. Yriel's spear is similarly written and ambiguous.
And can someone tell me why Tau had to loose their Target Locks?
Anyway, I think my Tau and Eldar where neither helped or hindered too much by the new edition. Thanks to allies there are ways to counter some of the new stuff. That said, Tau need some native anti-psyker and both armies need native anti-flyer to really be competitive.
I tried running through the Eldar codex to see if anything became magically playable. Eldar jetbikes went from "I need to get some of those" to "I REALLY need to get some of those". Warp Spiders maybe a little more useful thanks to hull points. A unit should be ably to glance most vehicles to death. Rangers, Pathfinders, and Dark Reapers all got a slight boost thanks to cover changes and precision targeting, but still not enough to offset their already over-costed points. All of them went from "no" to "maybe" in my list building process. Poor banshees will remain on the DL until Eldar get another codex. Harlies will remain in limbo until the faq is faq'ed. The new artillery rules would make the weapons platforms cool if their guns weren't so meh.
Mech Eldar took a bit of a hit in this edition thanks to the changes to objective taking. I can't fly around contesting like I used to. I also can't just put min squads of Avengers inside because I'll have to eventually get them out. I'm not sure what I'm going to do with my Eldar at this point. I'm thinking all foot, or foot hybrid. I'll need at least 3 squads of bikes whatever I do.
Eldar need a new codex in a bad way. 90% of the codex is over-costed, and 60% is outright unusable. It's a 3rd edition codex patched for 4th edition and we have to use it in 6th edition. Tau aren't so bad off. I can ally some orks or space marines; either with a flyer. Throw in an aegis defense line or bastion, and I'm 6th edition compatible.