Mercer from Imperius Dominatus here. I got my first game in against Eldar last night, nice to see what the Space Elves can do, even though I got my ass whipped in the process.
I have also now got the codex and had a quick skim. I'll do a quick first impression which maybe will be useful for people who have yet to play them or wish to know more info. I will get more indepth reviews up shortly.
* I will only be talking about units which interest me or I have looked at. So some units I won't be covering just yet, though please speak up about any cool stuff which I have yet to gloss over.
Battle Focus This is an excellent army wide (almost) rule Eldar get. It allows a unit to shoot and run or run and shoot. This allows you to re-position models into cover, closer to objectives or completely out of line or sight or even out of rapid fire range - pre-measuring is going to come in a lot when using battle focus. This is an excellent ability Eldar have, so if someone dumps their War Walkers out in the open expect them to do a pew pew and then run off and hide.
Bladestorm ALL shuriken weapons have this rule, basically a 6+ to wound is auto wound and counts as AP2 - nasty.
Autarch I haven't played against an Autarch yet, but I can see an interesting combo of mantle of the laughing god, fusion gun, firesabre and eldar jetbike. The mantle gives stealth and shrouding and re-roll failed cover saves - jetbikes get jink, so that's a 2+ re-rollable cover save. As Eldar jetbikes are fast and an Autarch has awesome ballistic skill, you could move up and use fusion to wreck transport vehicles and then assault with the firesabre; firesabre gives +1 strength and is AP3 and has soulblaze, which can effect units within 6".
Farseers and Spiritseers The Eldar powers are good, however there's two psychic power tables; runes of fate and runes of battle. The runes of fate tend to have two effects, one for Eldar units (which is a buff) and the negative effect for enemy units i.e Eldar get +1 armour save enemy units get -1 armour save - 3+ save Terminators anyone?
The Farseer is a mastery level 3 psyker and costs a very reasonable 100 points.
Spiritseers are mastery level 2 and cost about 30 points less, though they do allow you to mark an enemy unit during the movement phase and all wraith units re-roll 1 to hit. Doesn't say this ability is a one time use either. Note also makes Wraithguard troops :)
Exarchs Exarchs have been given more of a bigger status compared to the previous codex, which they just felt like squad sgts. Now they are superior Eldar warriors and can have a selection of powers, one power is called disarm which can make an enemy model lose their close combat weapon - handy for challenges.
Dire Avengers I really liked these in the previous codex and while they have gone up by a single point they are even better thanks to battle focus and bladestorm rules. They also have counter-attack for some reason, which is odd, but I am not going to complain.
Striking Scorpions OMG! These are just freaking awesome! They are roughly about the same points cost as previously, though they get move through cover, stealth and infiltrate as standard, previously you had to purchase an Exarch and then the powers to get these abilties. Their scorpion chainsword is also AP6; Tyranid little gribblies and Orks will cry. The Exarch weaponry is even nastier, chainsabres gives +1 strength, 12" shuri catapult and rending while biting blade gives +2 strength and is AP4, though the best is the scorpion claw, which is like a power fist, but is now a normal melee weapon - so will strike at initiative and will get +1 attack bonus with a shuriken pistol.
Fire Dragons Dragons got more expensive, but lets face it they needed a bump up in points as 16 points was way too cheap. Of course they get battle focus and now they get 3+ armour save so they are a little bit more survivable after those suicide runs.
Warp Spiders These bad boys really went up several notches in the new codex. They cost a cheap 95 points for a unit of 5 and their weapons have the funky monofilament rule; anything which is I3 or below or has no initiative then the guns count as S7. In addition 6+ to wound counts as AP1. Now the guns are only 12" range, but Warp Spiders can use their warp generators which moves 6"+2D6" - that's 13" on average. They then can run, which they can re-roll thanks to fleet - that's about 17" on average. Then Warp Spiders are jet pack infantry, so they get the 2D6" movement in the assault phase - that's a total of about 24" on average.
Crimson Hunter This is one of two flyers in the Eldar codex and I think the meanest of them all. It's entire purpose is to destroy enemy flyers as it has two brightlances and a pulse laser (S8 assault 2). You can throw in an Exarch making is BS5. It also has the vector dancer rule. Points cost isn't too bad, but it is only av10 and I can see lasting a single turn if things do not go well.
Windrider Jetbikes These are the re-named Guardian Jetbikes. They cost 51 points for a unit of three and get a 3+ armour save, which is way better than the normal Guardian save of 5+. They also got BS4 too along with battle focus and bladestorm. For a cheap scoring objective unit especially one which can move fast, then I think these are great.
War Walkers These are the daddy! They cost a little more, but weapon options are cheaper (all weapon options cost 5 points per gun except the EML), though best bit is they get a 5+ invulnerable save and are now BS4! These things will smash anything before them with the right weaponry.
Vyper An interesting little unit, but I haven't made my mind up about it. It has the same chassis as a D.E Venom and with a scatter laser and holofield costs 70 points, which isn't too bad, though I am wondering how much damage can it really do. Food for thought this one.
Fire Prism The Prism is a little more expensive now, but the prism cannon now fires three different shots; large blast AP3, small blast AP2 and a lance - not too shabby at all.
Wave Serpent Serpents can get pretty damn expensive if lots of wargear are thrown onto them, but they are very much worth it. The Serpent shield can now change a penetrating hit into a glancing hit on a 2+ or can fire the shield as D6+1 S7 AP- 60" pinning shots - though you do this and you cannot use the shield to change hits. Add in that the Serpent is now BS4, weapons are cheaper and it is a fast skimmer so can move 12" and fire scatter lasers (scatter lasers are awesome because if they hit all other weapons the model has becomes twin-linked) and the shield.
Holofield Thought I would mention this separately and because I have been talking about vehicles. The holofield gives +1 to jink saves, so 4+ cover if moved normally or 3+ if moved flat out. So it increases the chance of save from 33% to 50% and costs 15 points to do that. I am still up in the air about this, but it certainly does make Serpents more survivable.
This is about as much as I looked at/which interests me when I had a quick skim. As you can see just scratching the surface there's several good options. Discuss away or speak about things I haven't mentioned yet.