Mass Effect 3: Retaliation out now on Xbox Live

Retaliation, the latest expansion to Mass Effect 3's multiplayer, is now available on Xbox Live for the low, low price of nothing.

The free DLC is the largest to date, and features the return of the iconic Collectors from Mass Effect 2 as an enemy force. This brings the total opposing forces to four - Cerberus, Geth, Reapers and now the Collectors.

Players can face off against the Praetorian, Scion, Abomination, Trooper and Captain as part of the DLC, though a Harbringer-controlled Collector is absent. The Collectors bring with them a new Collector-themed Assault Rifle, SMG and Sniper Rifle, too. Cerberus and Geth troops also see an update with one new unit added to each force's arsenal.

Players can also take control of new character classes including the Turian 'Havoc Soldier' and 'Ghost Infiltrator' with more to come. Rumours indicate the Volus may finally be playable in a later update. Natural hazards have also been introduced to levels. Acid, Lightning, Meltdowns, Sandstorms, Swarms and Whiteouts will hinder embattled troops at random on a selection of the existing maps.

Finally Retaliation also adds "Challenges", which encourage players to keep track of their major multiplayer achievements, unlocking titles and banners players can use as bragging rights.

It's free. Go and download it, for god's sake. It'll be out on PC and PS3 at some point this week.