I have a special fondness for Subtlety, as my Rogue was Sub when he was was my main through much of Burning Crusade. He was my first toon to hit a then-current level cap. However, some time during Wrath, though I committed more fully in Cataclysm, I decided I liked the playstyle of Assassination more. I loved the idea of a Rogue stepping out of the shadows, striking, and disappearing again, and Sub's "focus on finishers" gameplay just didn't fit that fantasy.
Well, that's changing bigtime, thanks to a redesigned Shadow Dance and a new focus on Shadow damage. Poisons and Bleeds are now both Assassination-only (which I might cover eventually,) but while Stealth is still available to all Rogues, Sub's got a real clear focus on it.
As always, this is Alpha, so you can expect changes.
Let's get into abilities!
Backstab is still the main single-target CP generator, but it has been modified to allow you to use it while soloing. It does more damage when you use it from behind or the side, but it is still usable if your foe is facing you. Also, you can replace it with a talented upgrade at level 15 that removes any positioning elements if you still can't stand that stuff. It costs 35 Energy and generates one Combo Point.
Eviscerate is still your main damage finisher, and looks unchanged (though it's now Sub-only.)
Shadowstrike is a replacement for Ambush that includes a Shadowstep effect automatically if you aren't already in melee range. It costs 40 Energy and generates 2 Combo Points, and requires Stealth.
Shuriken Toss is baseline for the spec, giving you a ranged option, though I'm sure you'll want to remain in melee range when you can for auto-attacks and the superior damage of your melee strikes. It costs 40 Energy and awards 1 CP, and doesn't do anything to your auto-attacks.
The big change to the spec is that Shadow Dance is now a passive. Your finishing moves have a 20% chance per CP (so 100% if you use it at full CPs) to put you back into Stealth, which does not break from damage or auto-attacks for 3 seconds. It also summons a little shadow decoy for your enemy to attack (presumably so that enemies out in the world you fight while soloing don't just immediately reset.)
Shadow Techniques is a passive that gives your auto-attacks a chance to generate a CP, which gives a nice bit of variability to the spec.
Vanish gets the cooldown reduced by 30 seconds for Subtlety baseline.
Nightblade is your major "maintenance" finisher, a DoT that does Shadow damage and slows the target.
Master of Shadows gives you 60 Energy when you enter Stealth, which should make it very easy to pull off those Shadowstrikes when Shadow Dance procs.
Shuriken Storm is basically Fan of Knives, costing 35 Energy and generating a CP for every target hit.
Shadow Blades is your big cooldown, working just as it did in Mists by making your auto-attacks deal Shadow damage and making each of your CP generators generate an additional CP.
The rotation seems pretty straightforward.
1. Maintain Nightblade.
1. Shadowstrike (using either Vanish or Shadow Dance, the latter of which will go off very frequently.)
And then you can multi-dot Nightblade for cleave situations or in big groups, go nuts with Shuriken Storm. I wouldn't mind seeing some kind of Crimson Tempest equivalent, but given that there are still references to Fan of Knives and Poisons, I suspect that we don't have a totally complete picture here.
Still, tons of Shadow Damage and you'll be dipping in and out of Stealth constantly, which is pretty awesome. (Note: in PvP, Shadow Dance will merely allow you to use Stealth abilities - you aren't going to be un-targeting yourself constantly, as that would be way OP.)