There's a large difference between DA:O and DA2 in almost every aspect, ranging from combat to expansion on player choice to graphical improvement. What the game does right is it's expansion on the story. You have the choice of importing your DA:O save with pertinent choices that become small references throughout the game. With that said, it will not heavily influence any aspect of the game. This is somewhat disappointing because after such an epic tale, you'd hope there would be more cross over than "I met the hero who saved us from the Blight!"
The story is very well told otherwise, focusing on politics, religion, and connection to family. The choices are sometimes very difficult to make (no right or wrong choices) and the outcomes are very entertaining to play out. Voice acting is excellent. Graphics are superb (especially with some of the modifications with 4K textures).
Where the game falls short is in the combat/gameplay category, and this is very unfortunate. I played through on nightmare, and I expect it to be hard. I will state this clearly: the AI is horrible. No matter how I set up my tactics, the second I am not clicked on my current character, he/she will do something stupid to result in friendly fire and usually the death of someone. The only way around this is to disable all tactics except for attack player controlled target, and pause combat to assign special moves....which is okay and usually necessary on this difficulty. It makes the implementation of tactics useless when you're not controlling the character, and completely makes me lose interest in combat. I'll spend more time running away from Bethany's fireball or Varric's explosion bolt, or making sure Varric's arrow doesn't go through a boss while I backstab and take unnecessary damage. On the flip side, it adds an extra challenge, but it's more frustrating than fun after 60+ hours.
The other downside to the gameplay is the lack of customization. The DLC (gear) is great if you plan to play through the game multiple times as different classes. It's almost a waste otherwise as none of the gear can be placed on other characters (aside from some unique rings/amulets/weapons for early levels). On the same token, customization is SEVERELY limited for characters aside from Hawke (protagonist). This is really uncalled for as this is an RPG and one of the strong points should be customization. The same can be said about the skill trees - each character has their own unique branch, but otherwise it's pretty standard and boring.
I'm about to start Inquisition, and I hope it's deeper in it's gameplay mechanics and has smarter AI. Otherwise, I hope this review was helpful for anyone on the fence about playing through this sequel. It's worth it with a lot of patience.