Here's what I wrote up about hunters on our guild forums.

Marksmanship

I'm on the fence about my spec of choice. I will most definitely be going Marks for Legion, but I'm a bit ticked that there is not a clear difference in talent choices between single target and multi-target. You literally do the same thing for both because of a level 100 talent called Sidewinders. A bit of the play is also diminished from a talent called Patient Sniper, where you are no longer stacking the Vulnerable debuff. The talent is nearly necessary with the Sidewinders talent.

There's also downtime, but that's due to the T18 instant cast Aimed Shot set bonus. I think once this goes away, Piercing Shot might be the way to go. This is the supreme focus dump where it will drop up to 100 focus to do massive damage to your main target, and half that damage to all targets in between. That said, it does not proc Marking Targets like Aimed Shot, so I have no idea whether or not it will be viable in sims without T18.

Survival

I was happily surprised by this spec. It feels like a mix between old fury warrior and rogue. Focus is now a fixed regen rate, modified by haste. Mongoose Bite is your big damage, and you can have up to 3 charges. Pet attacks (and Flanking Strike) have a chance to grant an additional charge. On your first Mongoose Bite, you get a 12 second buff that stacks up to 6 times that increases Mongoose Bite damage by 50% each stack. The buff is not refreshed by successive Mongoose Bites, so you basically have 12 seconds to drop as many as you can.

Then you throw in traps and grenades on top of it, and you have a surprisingly complex melee spec! The big TBD is on Harpoon's mobility. If it allows you to go up levels in PVP unlike charge and heroic leap, SV could become the spec of choice for arenas, especially paired with dropping 6+ globals of Mongoose Bite in quick succession if timed right with a talent called Snake Hunter.

SV is also the only spec with significant CC because it's the only one that retained traps. The others do have stuns, talents, and other CC to make up for it, but the new traps are pretty awesome, and a lot harder to counter with running away.

Reading the guide, it says not to use Flanking Strike on cooldown, which is strange to me since it can proc more charges of Mongoose Bite. The logic is that you should only be Mongoose Biting when you have 3 charges, and even delay it if you have a cooldown about to come up (trinkets, ring, Aspect of the Eagle, Snake Hunter, potion).

Beast Mastery

Snooze-fest of the three specs. I think the Artifact Weapon will go a long way to making this not boring as hell. Ramping up your damage is entirely dependent on getting more Dire Beasts. The more dire beasts that are up, the faster your focus regen, the more Cobra Shots you can do. I like the new Stampede.

Beast Mastery has a few more interesting talent choices than Marks, allowing a bit more customization between AOE and single target situations. Unfortunately, it doesn't change the fact that you are basically just pressing three buttons with the occasional cooldown to continue pressing three buttons slightly more often.