I just got back from my local GW and I got a peek at the new Tau Codex. Let me just say that it is everything it's cracked up to be and then some.
I'll give you guys my highlights...
The Vespid
Look your doors and hide your honey pots, the fly men are invading. These guys look like they can really make an excellent highlight to a Tau army. They've got S5 AP3 guns, 12" movement, and Fleet of Wing. They are fast and deadly. My initial preception is that they can assume two roles: Harrasing an advancing enemy or shock troopers. They can jump on you by turn 1 or 2 and at Initiative 5 they'll cause most armies some problems early-on.
Kroot
The standard Kroot have remained more or less the same, probably for the best, but what really makes these guys great now is that their unit attatchments are no longer retarded. Kroot Hounds don't go running off after the first thing they see, and as such will not die horribly every game. Next is the Krootox. You can't infiltrate with 'em, but now they fall under the Fieldcraft rule. Turn after turn you can bombard your enemy with a Rapid-Firing Autocannon from behind 7" of forest.
Crisis Suits
A lot of the stupid issues with these things got resolved, chiefly that there is no longer a limitation on the number of Hard-Wired systems an individual Battle Suit can take aside from the 100 pt. Wargear limit ( ). Also, all hard-wired systems cost the exact same amount of points as normal systems, and Drone Controllers are free.
There are a lot of new "Special Issue" upgrades you can take, but each one is only one per army, such as the new mini-Ion Cannon blaster. Another neat upgrade you can take is a Self-Destruct button on one of your Battle Suits. If the unit breaks from combat the one guy with the upgrade stays behind, dies, and drops a S8 AP- Large Blast on your enemies.
One final note, Tau Commanders are now a 1+, so you always have to have one.
Pirhanas
These are gonna be a lot of fun. They come in squads of 1 to 5. They're Fast Skimmers, which in and of itself is enough reason to take 'em. In addition to that, when you disembark the Gun Drones they all disembark and form up into one squad. Basically zip up, blast away with Burst Cannons/Fusion Blasters and have your free squad of 10 Drones mop up the survivors.
Marker Lights
They get better. A lot better. Their new awesomeness is far too detailed for me to feel like writing.
Special Characters
Commander Shadowsun is pretty straightforward, no real surprises. The big guys are Aun'Va and Commander Farsight.
Aun'Va and his Bodyguards are a unit of uber-Ethereals. Each one of Aun'Va's guards has an Honor Blade and Counter attack on top of a very nice statline. Speaking of which, the entire unit is Toughness 5 and has a 4+ Cover save as long as Aun'Va is alive. Aun'Va sports some nice abilities himself, such as Supremely Inspiring Presence, it's like regular Etherals, but better. The big one though is Ultimate Price of Failure. If he dies your whole army takes a Leadership check just like normal Price of Failure, but in addition to that your whole army gains Preffered Enemy and Furious Charge!
Farsight makes a return in style. He himself is more or less the same guy as are his unit selection restrictions, but he does great things for your army. For starters, Ork Fighter does what it's supposed to: All your Tau get Preffered Enemy against Orks, and it's free. In additon to that anyone in your army with the option of choosing wargear (all your sergeants and Battle Suits) gets a Bonding Knife for free.
Anyways, there's the stuff I thought was really cool from the new book and you'll all see it for yourselves next month (or sooner). Enjoy