Going against that is nigh impossible, but Citadel does have a great campaign.

Dialogue in this DLC flows incredibly well, and the use of paragon/renegade interrupts is perfect. Besides all that you have cool moments like the car chase and what believe to be the most accomplish narrative storytelling in RPGs. Tela Vasir is also the best villain in Mass Effect, and both boss fights, against her and the SB, are also the best in the trilogy. I still remember playing it for the first time and being blown away. I think the mission part is superior in the former, especially the Shadow Broker ship, which might very well the most incredible location in the series. Picking between Liar of the Shadow Broker and Citadel DLCs is brutal. As a bonus, all the cool DLC (i.e., Leviathan and Citadel) would actually make sense to play.

When your setting is this good, you don't need or want to distort it with a civilization-shattering catastrophe. I will go to my grave insisting that ME3 should never have been about the Reaper war, but rather a hunt for a deux ex machina (the Crucible is fine) in the ordinary ME universe that could stop them before they arrive. It's possible there's an exception somewhere - I think I tend to play Citadal before Priority:Thessia, even though that freezes out Miranda, so maybe there's a natural break there? - but the fundamental problem is that the Citadel DLC channels the best parts of Mass Effect (the characters and setting), and ME3's 'total war and genocide are no fun' plot actively undermines those things.

There's always something absolutely awful happening, and it's always urgent. There is more or less no logical time to do it, at least in my memory of playing ME3, because there are almost no natural lulls in ME3's pacing. I think the narrative dissonance with the Citadel DLC highlights mistakes made with ME3's plot and pacing in general.

Mass effect rendering thread exception