Long time player, newly on this forum (mainly for some more Eldar-centric topics).
As to the new codex, there is very little I do not like. One thing I do not like is Karandras not having the Stalker special rule the Striking Scorpions Exarch has. Every other Phonenix Lord has the special rule of their corresponding Exarch (or a better version of it in one form or another)...except for Karandras. Lame. The only other thing I take issue with, and it is really one of personal preference, is Dark Reapers having any main weapon link to the weapons of Asurmen/Dire Avengers. Seems hard for them to break from Jes's original concepts (however, they did drop the Web of Skulls), but they really should. So, no shuriken cannon option for the Dark Reaper Exarch, and the Maugatar should be changed to a bad-arse reaper launcher with the executioner blade on it. That would serve to fully differentiate and unify the Aspect, just as the others are.
D-scythes weapons are bit gross (only because of the multiple auto-hit feature), and I wouldn't be surprised to see them with a -2 penalty on the chart roll next time around. Such 4+ death would still be vicious enough.
Otherwise, The Windriders and Skyrunner Warlock/Farseer kit looks good. I could have done without the Warlock bits on the skyrunner kit, and instead would have liked more Farseer details/bits on the kit. The main reason for that is because Skyrunner Warlocks could be better served in another way, that being making a Infantry Warlock kit which includes Skyrunner legs/arms, and then you just buy the Windrider kit to finish them off. Ah, but then it wouldn't cost us $33 per model. And we'd have a Warlock kit with way too many options.
The only thing I might also have like to have seen were some tiny decorative bits for the Windriders- perhaps riding jackets/sashes; something simple to break up the armor (and colors) on the models.
The Autarch is a great looking model, but functionally he is at odds with the army he is a part of. Rules-wise, the Autarch is Aspect-ish, but not enough that he can hang with any Apsect in its area of expertise. The one Aspect he can bolster are Swooping Hawks in that he doesn't screw up their deployment (he being able to have Swooping Hawk wings too), and he can bring some good, ranged, heavy firepower to bolster them. The new Autarch model is, however, armed for close combat, and so is equipped counter-purpose to what Swooping Hawks are wont to do in combat. So, that leaves us with two uses for this nice looking model- he drops in with Swooping Hawks and then jets off on his own to wreak havoc, or he joins some other squad on foot and jets off on his own when appropriate to wreak havoc. Either way, he is more of a suicide type character, there not being any unit in the entirety of the Craftworld Eldar Army that suits the tactics indicative to how this model is equipped (Shining Spears come the closest). Doesn't mean there isn't still fun to be had with him though. The main things I like about the Autarch model are the Swooping Hawk Wings and the mandiblaster helmet, though not for the rules they provide. What I like about them is that they are a glimpse into what (hopefully) lies ahead for plastic kit releases for Swooping Hawks and Striking Scorpions.