Some BIG improvements mixed with a few disappointments - overall a very solid expansion.
Basic Information
1. Game length is appx 20-30 hours depending on how long you take with side quests, re-spec-ing characters, etc. The main playthrough is 3 quests plus 1 final quest, but each quest is shorter than DOA quests. ie, in DOA Deep Roads quest you had 2 seperate quest lines - Castless Quarters + Branka - in Awakening each quest is just one part. So overall the quest length is appx 1/3 or 1/2 of DOA.
Improvements + Pluses
1. New spells, skills, and abilities - there are some great new ways to spec all of your crewmembers - specifically more ways to combine melee and magic, as well as improved stealth techniques, and thankfully more ways to be an interesting elemental character
2. Manual of Focus - infinite manuals allow you to endlessly respec your characters from the ground up, including stats, ability, skills, the whole 9 yards. very nice so you can try out new character sets for endless variety
3. Tons of new weapons and armor - really helps you feel as powerful as the story makes you out to be
4. Side quests are more interesting for sure, and are less run here run there
5. Being in charge of the Vigil is sweet. Awakening has some really interesting scenes where you rule over your subjects, and building up the keep has a great feel to it - very very solid
6. Some great tough choices to make - and some nice twists - the story is as good as ever
7. In general, the boss fights are more frequent and are staged better. With the exception of the final boss, which i thought was weak overall, not in terms of story but in terms of strength, which i address below
8. The artwork is darker and the levels laid out better. Each area's design is rather superb.
Disappointments + Minuses
1. Overall, the game is easier. this is the case in spite of tougher enemies in many cases, but with great new skills, spells, and equipment you'll likely need to bump it up to hard if you were on normal, or very hard if you were just playing on hard like i did through DOA. overall the game feels a tad too easy. Also, there are less huge room battles i think, so less times where you're totally swarmed with enemies.
2. Companion characters are fun, but less involved. there's less character conversation to be had, and as GS notes, none of the characters are as good as Morrigan or Alister. They're not bad, however, and are fun to play with. they're just not quite as good as the originals
3. Quests are shorter. Comparing this DLC to Fallout 3, Fallout gave you more hours of play for $40 than Awakening i believe. this is debateable, but it'd likely stand by it.
4. You're significant other from DOA won't be around this time which is kind of odd - furthermore there's no romance.
Overall
Very solid expansion with enough pluses that if you liked DOA, you'll likely love the expansion. In general, it's very fan-oriented with the ability to re-spec characters etc. So if you're a fan, you can't go wrong with Awakening.