DAO is a great game if you like older RPGs like Baldur's Gate and the like. But it's long, at times slow, and doesn't play well on console.
DA2 is a good game if you like action-rich RPGs and it plays far better on console than on PC. It's not as phenomenal as most other games by the developer, but that still makes it a good game. DA2 also has no direct links to DAO and the character has no knowledge of anything that happened in the first game. It's the same world, but mostly entirely seperate games.
I played through 1 once, and got maybe halfway into the Addon, but I don't think I'll give it another try. DA2 is something I like to get out every now and then as it is much faster paced and gameplay is more exiting.