I love the main game, but the actual expansion really started to show signs of lazyness, and what was to come in DA:2.
I played through the main game 5 times, and thrived on each playthrough, with it never getting boring. But I only played through the expansion twice, first time I was bored after about 2/3rd, 2nd time I quit halfway through.
The seperate DLC's were a mixed bag. If you're thinking of buying them here's what I reckon........
Warden's Keep
This is a nice side quest that will net you a couple of pluses for your overall game. There is a nice armor set and a a robe that improves Blood Magic. Also, there is something called a "Party Storage Chest" that will allow you to keep excess items you don't want to sell (very useful). Finally, there is a smith there who sells the highest grades of weapons and armors (without bonuses) so you can get really good equipment early in the game, assuming you have enough money for it. An advantage of this is that sometimes (not always) when you sell the smith a lowered-tier weapon or piece of armor, he'll upgrade it to a tier 6 or tier seven. Only drawback is that you'll have to purchase it back at a much higher cost. Lastly, the story is pretty good too.
The Stone Prisoner
I'd get this just for the fact that the playable character Shale (a golem) is really funny. Also, they managed to integrate Shale into the main storyline almost flawlessly. I've had one play through where the golem was my main tank for the entire game and I didn't notice any glaring errors where the programmers "forgot" to include him/her/it in a scene. The quest to find Shale is ho-hum however, the voice acting and the dialog are wonderful. I can't see myself playing Dragon Age without this DLC.
Return to Ostagar
This one isn't bad either. You return to the battleground from the battle where Loghain deserted the Grey Wardens. You collect King Cailian's armor, which were distributed amongst the Darkspawn generals and eventually fight the Ogre that killed the king. This fits right into the main story and the armor, sword and shield from the king are very nice.
Feastday Gifts and Pranks
You don't need this. All this allows you to do is to easily manipulate the approval rating of your party members. Each gift or prank can heavily influence, positively or negatively, the approval ratings of each party member. It does 0 for the story and only makes a tiny difference to the game play.
Darkspawn Chronicles
This one is a lot of fun. You get to play as the Darkspawn and can eventually control every different type there is. Genlock's, Hurlock's, Ogre's, Shrieks, to name a few. Also, you get to fight the Grey Warden's companions. So, if you've ever wanted to play as the bad guy, you should get this.
Leliana's Song
Too short for my taste, but a nice addition and gives some good backstory to Leliana and experience the events that inspired her to join the Chantry, several years before Orgins. It also has a transferable reward for both Origins and Awakening. Even though I want it to be longer, I like this one too.
The Golems of Amgarrak
I am not a fan of this one. There is almost no story and the entire thing was made to challenge the better players out there. I am not one of the better players out there and as such, I found this to be very difficult on the Normal setting to the point where I eventually gave up. If I ever decide to improve my skills, maybe I'll take another crack at it, but I play games to have fun, not to rip my hair out.
Witch Hunt
I am not of fan of this either. Again, this is too short and the story is pretty bland. In this one, you investigate Morrigan after the events of Origins. Like in Leliana's Song, rewards that transfer into Origins and Awakening, and that it is the final DLC to be released for Origins. This is supposed to bring closure to Morrigan's storyline, but the whole thing feels rushed and unsatisfying.