Level 49 after 25 hours on PC and level 22 on PS4:
A million miles ahead of Advanced Warfare which was gash, unlike AW the movement in Black Ops III doesn't massively hurt the gameplay, I'd still prefer boots on ground gunplay but I can live with the thruster, although thrust jumping should throw off your aim a bit to deter people from doing it mid gunfight.
One thing they've done so right, which most CoDs struggle with is weapon balance, I had 5 different guns and swapped between them often with no difference in ratio. It's unlikely you'll ever see the majority of a lobby using the same weapon outside of the first few days.
The Specialists are fun, but the weapons are too strong on PC, especially the Annihilator, Sparrow and Tempest. Rejack should be reworked entirely as dead should mean dead, Last Stand and similar are always unpopular as they're a crutch perk for noobs to kill better players. I really enjoyed Vision Pulse and Active Camo.
Maps are great, although the B flag on Combine is way too open, probably the hardest to cap flag ever. I can't wait to see more, and I'd love a Treyarch classic pack (Firing Range, please).
Graphically it's nice, although I couldn't play it maxed out due to performance issues and extra textures were not playing nice. I assume this will be fixed at release so the game will look much better then. Presentation is top notch, the UI, menu and HUD are all fantastic. The Specialists all look unique and very detailed as well.
Performance was OK for a beta, some stuttering and I had to turn some settings down for 120fps which I shouldn't have to do but PCDev has assured me Black Ops II ran way worse at this stage, and that ended up running perfectly for me so I'd expect the same from Black Ops III. There was some issues with mouse accuracy though, even with acceleration and the like disabled, hopefully this will be fixed before release.
Overall it's a solid package, and easily the best CoD since Black Ops II, and I will be definitely be buying it for PC. Doing a beta was very smart, as I wouldn't have bought it after Advanced Warfare being so bad. If they can fix the niggles (Flinch is OTT, non lethals last way too long, some scorestraks are really bad for their cost) then I can see myself playing this for hundreds of hours.