Okay, I'm going to try to sum this up as best I can.
What I liked:
-Wrex, not including him as a squadmate in either of the sequels was a huge disappointment for me. It's great to finally have him back.
-Lot's of often funny character driven dialogue.
-Urban area combat, this is something almost completely missing from ME3 where seemingly every mission takes place in a War
Zone.
-Cool new enemies who could so easily have been just more Cerberus troops but aren't.
-Extra cut scenes for each character, that aren't tied to the main story in some convoluted way.
-Lot's of additional little mini-games and an arena like game, giving this DLC lots of replay value.
-I thought the main villain, if a tad far fetched, was actually pretty creative and interesting. And the twist was good as well.
It gives every single character a chance to shine and plenty of dialogue, nobody is shafted, not even characters like Kaiden, Ashley, or Javick who it's unlikely are even there.
What I did not like:
-There were lots of jokes, not all of them were winners for me and some of the dialogue just felt cheesy and out of character for Shepherd and his/her squadmates.
-As much as I appreciate the gesture, the idea of Anderson buying Shepherd a penthouse to "unwind" when they're in the middle of a galactic reaper invasion is just too absurd for me. I get that this DLC is kinda playing it loose with the story but this is still technically ME3 canon here. Besides, isn't Shepherd's real home supposed to be the Normany?
-I know they did it to give the gameplay some variety, but you know you aren't going to have much fun when your mission objectives involve "looking casual" and "mingling" with people.
-I said I like the main villain conceptually, and I do, but I don't care much for bosses who's health simply reheals every time it gets too low, forcing you to defeat them in some other arbitrary way that isn't made clear.
-While it's totally optional, I find it almost insulting to think that Shepherd would be spending time partying and gambling while billions of people are dying all across the galaxy. In fact this whole DLC would make SO much more sense if it was set AFTER the reapers were stopped. Maybe killing off Shepherd at the end wasn't such a great idea, Bioware.
Overall Impression: ME3s ending, though not in my opinion all that horrible, was pretty heavy and didn't give the characters any sort of proper send off. At some point during the volcanic shitstorm following it's release Bioware decided to stop playing dumb and try a new strategy of actually acknowledging what the fans were saying they wanted. Citadel is their attempt to steer in the complete opposite direction of ME3s ending and give fans what they've asked for by the truckload. And while I think at times it goes a bit overboard and smells quite strongly of fan service it you simply can't deny the quality and effort that was poured into this DLC. Had this actually been a post credits ending to the game it would have been a damn good finish to the series, as it stands it's a decent patch to the open wound the game left in most people and is a must have for any fans of the series left cold by the ending.