I haven't been on the beta much but today I messed around on all 5 of the classes I've created to try to get a feel for how things have/haven't changed.
Hunter is the most interesting to me at the moment thanks to pet changes and Marks being redone. Marks is playable now (I DESPISE Legion Marks. I can't over exaggerate how much I loath it. I did the Marks artifact weapon scenario as BM.) Vulnerable is gone (GOOD RIDDANCE) and I actually feel like a sharpshooter instead of spraying and praying. You have four main abilities, without going into to much detail two of them generate focus, two of them spend it and you can really affect your play style by what talents you choose.
Pet changes: I currently have five pets on the beta, basic models selected by Blizz. Scorpid, Turtle, Cat, Dog, Bird. Cat and Dog are Ferocity and as we were warned you can't change the spec of your pet. Turtle and Scorpid are Tenacity, Bird is Cunning. Each family had a special ability that goes on your bar (it's called Command Pet if you have no pet active), the Ferocity family gets Primal Rage (aka Heroism/Time Warp), Tenacity family gets Survival of the Fittest which is a damage reduction cooldown for you and your pet. Cunning gets Master's Call.
Lots of random bugs still like numbers changing on talents as I am staring at them and my Bird refusing to go away when I dismiss it or the bird coming when I summon another pet (called the dog and had dog plus bird out just now).