Well, thankfully Arms is starting to look a little more like it did in Mists of Pandaria. The spec is still relatively simple, but most specs are getting trimmed down that way.
So what have we got?
None of your abilities actually generate Rage, but at least on my transferred-over Arms Warrior (who, with some demonic invasion gear, is ilevel 692) I've been getting enough Rage that it's very rare that I run out.
Colossus Smash is still a core part of the rotation, but they've brought back the proc passive, called Tactician now instead of Sudden Death, which will give you a chance based on Rage spent to reset the cooldown of both Colossus Smash (which is baseline 45 seconds) as well as Mortal Strike (baseline 6 seconds modified by haste.) Colossus Smash no longer has you ignore armor, instead it simply increases the damage you do, which I presume will be easier to tune, especially in PvP.
Your new Mastery, Colossal Might, increases both the damage of Colossus Smash as well as the damage bonus, so this is a pretty central thing.
Mortal Strike is the center of your rotation, hitting harder than anything else except Execute. It's on a six-second cooldown, but you'll always have it up when you get a Tactician proc. It still applies a healing debuff and costs 20 Rage.
When Mortal Strike is on cooldown and you have Rage to burn, your single target option is Slam. This does not do as much damage, but it has no cooldown and costs 15 Rage. This is absolutely a filler, but it's nice to see it back in the core rotation.
You don't have a ton of AoE abilities, but you can play a little bit in talents.
Whirlwind is your main AoE Rage dump, basically just taking the place of Slam in your rotation. You also get Cleave, which is on a 6 second (reduced by Haste) cooldown and costs only 10 Rage. Cleave hits any number of targets, and it will buff your Whirlwind to do 20% more damage per target hit, up to 5 stacks (so in a group with five enemies, you can get it to hit twice as hard.) There is also a talent that makes Mortal Strike and Execute cleave to another target (man, are we going to have to start using a different term for Cleave damage now that Cleave is straight up AoE?)
There's lots of abilities you can add to the rotation through talents, like Overpower (similar to how it used to work,) Rend (likewise,) and Focused Rage (a stacking buff you apply to your next Mortal Strike.) It's still not super-complicated, but there's definitely more finesse you can work into the spec now, and it has very strong survivability while soloing.