Had some extra cash on hand so I finally broke down and bought Omega and Citadel. Don't really have much to say about Omega, horribly mediocre. Carrie-Anne Moss was just phoning it in (not that Aria was terribly expressive to begin with...) As for Citadel, Fan. Fucking. TASTIC. Won't rehash everything discussed here already, but suffice it to say I loved every second of it. Best DLC of any game I've ever played, and also the hardest a video game has ever made me laugh.
I think my personal canon on all future playthroughs shall be to play through all of ME3, including the ending, and then play Citadel, pretending that it's Shep's own personal, happy slice of the afterlife because a) it's so tonally different from the rest of the game and b), seriously who wants to slog through Cerberus HQ and Earth AFTER playing this masterpiece?