Ironically, with Dragon Age 2 BioWare made a game closer to Dungeon Siege than Dungeon Siege 3.
The party based action combat and skill trees are there all already, they should just add multiplayer and change "Kirkwall" to "Stonebridge", "Templars" to "Azunites", "Thedas" to "Ehb".
Oh, and cut 90% of party banter, voice-over that's even worse than Dungeon Siege 2, and all romance BS.