To begin with, this is a great and worthy expansion. If you liked the original game, you will like this one, no doubt. It's tailored in the very very same fashion.
That said, it has a huge burden over its shoulders: the original game was TOO good. Most people have even played Mass Effect 2, also from Bioware and very similar to Dragon age, and Mass Effect 2 is damm good. So, for this Dragon Age expansion pack everyone is expecting it to be even better. We want a lot of characters, and we want them to be great. We want loads and loads of gameplay hours. We want new weapons, new scenarios, new enemies... We want, to sum up, Dragon Age 2. And no, this isn't Dragon age 2, this is "just" a expansion. No more, NO LESS.
You can keep your Dragon age character, thus carrying over "all" your decisions made back then, or you can create a new character. If you import, you are a hero after all, so people look upon you like that; if you create a new character, you are just a grey warden no-one has ever heard about. Your decisions in the original game and your character change some parts of the game, but even then it's not such a big change.
You made a lot of decissions, some of them early in the game, and they all shape the way the game ends. Again, its just like the original game. If you liked it back then, you will like it now, for sure.
The new characters are nice. You may like some more than others, but anyway, they are well-written. If any, I personally think the game lacks of a OUTSTANDING character, just like Morrigan was to me in the original game. They are all, as the overall game, "just" great.
Just a very bad point: the game currently has a lot of bugs. Some of them are forgiveable, like some graphic glitches; but there are other killer ones, like "falling outside of the world" or getting stuck in a loading screen, both forcing you to load a savegame, God knows when it was saved. Those are not forgiveable. They will be fixed, though.