Last minute information about Dragon Age: Origins - Awakening continues to trickle onto the web, with the most recent preview surfacing over at AtomicGamer.
So you'll always come in as the new commander of the Grey Wardens, you'll see a somewhat different game as a new character versus an imported one. And if you didn't complete Origins, you can still import into Awakening at any time - although it will plug in some bits for the ending of the original game just for the purposes of starting the campaign. The saves are kept separately and you can still go back and finish Origins whenever you want, even after starting the expansion, but it will be right from when you exported your Origins character - you can't go back in time to non-expansion content with the Awakening version of your character.
Of course, your character will go through some changes in the expansion. There's a full range of new loot, spells, skills, and specializations, the level cap has increased to 35, and there will be new "epic" versions of abilities. Players will also be able to customize runes and also now add them to armor, allowing for much more customization than before. The developers didn't go into much detail and I didn't get time to start writing down names of all the new stuff, but it seems reasonable to believe that BioWare won't disappoint here.