The full game will also be releasing outside Steam with no DRM, but the beta uses Steamworks because it's "a far better environment" to test the game in. Bedrock Beta includes a sandbox map.
There's also the Goodly Conflict where a hero fortress lies in the centre of the map and you'll have to fight your way towards it for riches. There'll be a third option later.
Confirmed in the Bedrock Beta:
• Rooms: Lair, Treasury, Slaughterpen, Archive, Foundry
• Spells: Summon Worker, Possession
• Minions: Blood Imp, Gnarling, Gargoyle, Augre, Cultist
• Heroes: Firebreather, Juggernaut
• Game Systems: Digging, Fortifying, Gold & Mana, Portals
• Unit Systems: Hunger, Sleep, Basic Combat (no abilities yet)
For more information on how to get a hold of the Bedrock Beta visit the official War for the Overworld site.