The Mass Effect trilogy is over. In spite of the fact that the ending remains unchanged, the release of the new Citadel expansion pack provides fans of Shepard and the crew of the Normandy no small amount of closure for their stories and their adventures.
It isn't the be-all end-all of expansion packs, and there's certainly much to be desired about the ending to Mass Effect 3, but it goes without saying that BioWare has even more things planned for the franchise, which has thus far proven to be their most successful, if not most lucrative series to date.
Gamers who've played through the Citadel may have noticed what could best be termed a "suspicious" amount of backstory regarding the First Contact War in the DLC. The content clearly written for the DLC, and not something the studio had laying around and decided simply to put into the game. There is a good context for it being there, and we—like many fans (via reddit)—are speculating that the backstory serves as foreshadowing for what BioWare has planned for the series.
The First Contact War itself is a bit of a misnomer, as less than 500 were said to have been killed in what the Turians themselves prefer not to refer to as a war. Yet even so, there's a good chance that we don't even know the half of it, and the story could focus on what happened behind the scenes, as it were.
We'd prefer for the series to move forward, but given the fact that BioWare may have written the story into a dead-end with its endings means that we'd have to experience more of the Mass Effect universe "as it happened"—unless they opt to make one of the game's endings canonical, that is.