Aside from beta access, the pack includes three heroes: Tyrande, Diablo, and Raynor, each with an alternate skin. Diablo gets to look fishy, Tyrande gets to look like a Blood Elf, and Raynor takes all of that high-powered armor off (which seems like a bad idea on a battlefield, but I guess that's why I'm not a space marine). You also get a mechanical golden wolf mount to ride around on the battlefield and 2500 gold for the game, which is more than enough money to buy anything that costs less than 2500 gold. Check out the pack trailer just past the break.
[Thanks to Siphaed, deathandtexas, and Vincynt for the tip!]