Well, finally I have a chance to read through the codex, so I spent the night doing so, and will probably spend my Friday doing quite a bit of the same.
My first thoughts are that this is a very complex codex. With so many new powers, units, and weapons, that it is going to take some serious time to digest. It also will be hard for people to know really what is coming at them. There will be a ton of fail with this codex, and for that simple reason it should not be a tier 1 competitive codex. You will see tier 1 competitive players winning a lot with it. We will see who the true players of this game really are. It will be a hard codex to master, and after reading once through, that task seems supremely difficult (and fun).
Beast Masters. Wow, they really stood out for me almost immediately. A multi stat lined unit, with great choices for beasts. I'm not even sure this unit will work well, but from first impressions I like what I see. The problem is that they are competing with other good units, like reavers and scourges (they get a 4+ save now and good weapon options)
Heavy choices. I found these a little more difficult to find the benefits from first glance. Razorwings and Voidravens sound and will look cool on the field. However, once you do something like add in missiles to the voidraven and an upgrade you are hitting 200 points, and if you like implostion missles (who wouldnt) 30 points apiece. wow. I found myself looking back at the Ravager as a better gun platform. Who knows though, you could field the voidraven without the missiles, and then your talking 2 void lances. Str9 ap2 lance shots.
That's all for now. I have to get some work done this morning, and sneak in some reading.