Opening Story Mission - Here you can play Homecoming, the opening story mission of Destiny 2 that was originally shown off at the gameplay reveal in LA.
Two Crucible Maps and Modes - The classic Control will be playable, as well as the new Countdown mode, which is attack and defend based. For PC players Javelin-4 will replace the Midtown map.
Inverted Spire Strike - The co-operative Inverted Spire Strike was another aspect to be shown at the gameplay reveal in LA.
It should be noted that these specs can change from the beta to the full game, when Destiny 2 eventually releases on PC on October. Bungie have stated as much in the official announcement post on Bungie.net, where the developer warned players that the PC specs for the beta might not necessarily be the same for the full game.
Destiny 2 PC Version Detailed
Towards the end of the game play reveal shown on May 18, Activision announced that Destiny 2 would be available for PC players exclusively through Battle Net, with players being able to find each other through the online service.
In addition to this, it's possible that Destiny 2 on PC will run at native 4K resolution, as well as 60FPS uncapped.