The advancements in RPG mechanics would be enough to set it apart, but the real achievement of Dragon Age II is in the story-telling. I could point out the improved combat and graphics till there's blood covering my face, but BioWare is one of the few companies that uses the advanced computing power available to modern game designers to let you actually play a role.
Dragon Age Origins was an enormous mouthful in a time where huge games are a rarity. Dragon Age II is somewhat shorter, but nevertheless a big game with an exceptionally well-framed story. Most of the new additions and updates are welcome, even if they don't put the game at the front of the pack. Easily recommended.
It really seems like the biggest mistake is calling it "DA2," as it's just different enough from Dragon Age: Origins to not feel like a sequel, but more like a reboot. The different main character, the faster and more streamlined combat, and the overall structure makes it feel like a fine Dragon Age adventure, but not a direct follow-up to DAO.
Despite its game mechanics being streamlined to cater the console-audience with a high tempo and a smaller set of statistics, Dragon Age II is still a massive role-playing adventure. With its immersive storyline and good class system, it its yet another Bioware game in the collection of great role-playing experiences.
Defying all expectations, BioWare managed to take one of the most memorable Western RPGs in recent history and completely destroyed everything that made it so good.