Absolutely Mediocre, half done and rushed...
Since KOTOR I haven't seen any story really good (and NO, I didn't liked Mass Effect I, haven't played Mass Effect II yet, though), but Dragon Age Origins is awesome, once again we had an original, epic RPG game, with a lot of spells and abilities, many beginnings and great NPCs companions, BUT do not expect anything like that in Awakening.
The game is half-done, most fighting is fine, why not, the engine already exist, it doesn't even have a proper ending to tell you the truth. A lot of quests ends suddenly, like finding stuff and as soon as you get it, that's the end of it, giving you a sense of incompleteness and meaningless task.
My point is, after Origins, getting a second quality expansion, after an end battle of such epic proportions played, my god, don't do that. Is like having a movie at the cinema and then jumping to the TV Show version, with second class actors and second class special effects, lol.
The plot is also too similar to Dragon Age Origins, you have three main places to explore, the forest, another part of the Deep Roads and a haunted town, once you do that, yo go to the final battle. First there is no logical connection why the final battle happens after these 3 quest, although it is obviously expected, second the final battle is almost as trivial as any other fight you already had on the game.
No to mention, you can't even talk to your companions, they talk to you as the story goes and you give them gifts, but when you talk to them, you don't get a conversation. Their stories aren't that interesting, one of the characters (avoiding spoilers here), was meant to hate your, after a couple of gifts, he is the one who loves you the most, kinda ridiculous
At the end, for me seems obvious they rush to give us a expansion just for profits, I don't feel offended about good companies making good money, but not sacrificing so much quality. If you loved Dragon Age Origins as much as me, might consider not getting the expansion, so you'll keep for yourself the best flavor of Dragon Age OR get it, to have some extra fun, but keep your expectations very low, so you can get some fun extra-missions without being disappointed.
PD. Where the hell was my Mabari... he was my best fighter in Origins