What's the price of all the DLC combined, and how does that compare to the content of a traditional full expansion?
Main campaign:
Warden's Keep $7
Feastday Combo Pack $2.99
Alternate Campaigns:
Witch Hunt $7 (?)
Golems of Amgarrak $5
Leliana's Song $7
Darkspawn Chronicles $5
Return to Ostagar ($5) and The Stone Prisoner ($15) was free, so they can be seen as a part of the main game really, just like Zaeed Messani in Mass Effect 2. You should have them already. Return to Ostagar brings some closure to what happened there, a nostalgia ride similar to Normandy Crash Site for Mass Effect 2. I like Stone Prisoner. The golem is one of the best companions in my taste and also one of the funniest.
Warden's Keep gave me an ability to draw mana from my hitpoints, which was useful as mage, and it also offers a Party Chest which really should have been in the main game. That chest alone made the DLC worth it for me, the rest wasn't that interesting really.
Feastday pranks was meaningless if you ask me. Waste of inventory space.
Witch Hunt and Golems of Amgarrak could be played with the Warden, which can be seen as expansion material. You can import your Warden into Golems of Amgarrak, but you cannot import him/her back to be used in Awakenings. Beating it will give some really nifty rewards which I actually used throughout Awakenings.
The game is very difficult with a low level character, but even with my level 34 warden, the end fight on hard took several hours for me (you get an achievement for beating the end challenge on hard or greater difficulty). The DLC is very atmospheric and immersive in the first part, but then I thought it became more about solving puzzles and crawling through monsters.
Leliana's Song and Darkspawn Chronicles are games in themselves. Darkspawn Chronicles was an "alternate universe" style of story which doesn't intrigue me. Leliana's Song was quite decent if you accept that you are playing a story rather than creating the story, that is, the story is ultralinear without much of a choice. If you like the companion you should check it out. It's quite challenging because you are going to play it all at really low level and every goldcoin counts.
I have to say that none of the DLC's have been a must have or could match the quality of Overlord for Mass Effect 2 or Point Lookout for Fallout 3 which I consider to be the best DLC's. You get some brief entertainment out of them but nothing really memorable.