IF you can't end a game properly, the least you can do is blow it one last bittersweet kiss. That seems to be BioWare's realisation with its release of Citadel, anyway.

This final downloadable chapter for Mass Effect 3 draws the curtain on the game a year after its release. And it concludes a science fiction role-playing trilogy that started six years ago.

Citadel is set on the giant space station of the same name. Chronologically, it's set in the middle of the Mass Effect 3 story, and it might seem odd for a developer to devote so much effort to an interim episode long after most fans have finished the game.

But it isn't so strange in Mass Effect 3's case. The original ending of the game was a letdown because it resolved the plot poorly and gave short shrift to characters that gamers had come to love. And although BioWare made the unprecedented concession of releasing an Extended Cut to placate critics, there are only so many improvements once can make by tweaking an ending.

And so we've got Citadel, which has Admiral Hackett ordering your character, Commander Shepherd, and the crew of the Normandy frigate to the Citadel for enforced shore leave so that the ship can be repaired.

There's a central mission that comes across as a bit of a mash-up of The Sims, Star Wars: The Force Unleashed II and Skyrim: Hearthfire. But it's all really an excuse for you to spend lots of time with friends and lovers in a recreational setting drastically different from the usual setting of a warship constantly on battle alert.

In fact, you get to spend so much time with your buddies, and explore such unexpectedly different sides of them, that the whole chapter often feels wildly improbable.

What are the odds that your entire crew, past and present, are on the Citadel at the same time? And while everyone is different when off-duty, some of the horsing around is out of character. But the overall experience is so emotionally satisfying that most fans will find it quite easy to suspend disbelief.

Hang out with Talia to watch alien soap operas. Challenge James to break his record of 182 chin-ups. Dance with Garrus at a nightclub. Challenge Ashley to a drinking game. And let everyone give you grief for destroying the Citadel's best sushi restaurant.

In-jokes litter Citadel, and extend beyond the Mass Effect universe to pay humorous tribute to sci-fi classics such as Orson Scott Card's 1985 novel Ender's Game and the very first 1977 Star Wars movie.

There's so much cheekiness, in fact, that it's easy to overlook the serious bits such as the chance to properly explore romantic relationships that get stifled on the Normandy. It's tender and moving stuff, and all the more bittersweet against the bleak backdrop of interstellar war.

The climactic portion of Citadel is a house party that gathers everyone in a posh apartment Admiral Anderson has given you, and sees even the most hardened soldier embarrass himself or herself after a few drinks. If there's any doubt that this is goodbye, it's banished when the team huddles for a group photo. The morning after, the team sombrely readies itself to return to battle, and your lover leans on your shoulder to tell you that whatever happens, you've had a good run. For gamers, it's been an extraordinary run, in spite of the stumbles.

Some might have initially questioned the wisdom of releasing some of Mass Effect 3's best content as downloadable chapters set mid-game, long after fans would have been done with the ending. But they've cumulatively made up for the lacklustre ending. Leviathan provides valuable context for Mass Effect's war against the relentless Reapers. Omega lets gamers explore that criminal world. Reckoning adds guns and monsters. And now, Citadel showers the characters and story with the kind of loving obsession usually reserved for fan fiction. Nice job, BioWare. With this final chapter, you've redeemed yourself.

Citadel is available now as a download from Origin, Xbox Live and the PlayStation Network.