Citadel DLC can be summed up in three words -
Wrex and Tali (assuming you get the conversation with Wrex at the bar. THAT is the most hilarious conversation I have ever heard in a game. Although, a drunk Tali comes close)
The mission was cheesy - wasn't expecting anything much either way. So, no disappointments there. I was more looking forward to the character interaction and this DLC does an amazing job of that.
I would suggest playing it after completing the main game. Since, as was mentioned, it is in very stark contrast to the theme of the main plot. That aside, I have to say, the DLC content for
ME-3 is pretty good and meaningful, I suppose.
One question though - How the hell does Barla Von have the highest score in Armax Arena till you beat it?