BIOWARE IS FINALLY DELIVERING on the downloadable-content promise of the original Mass Effect (which itself only received two DLC offerings in over two years).

This time around, the DLC has come thick and fast, with five mission-based packs and many more armour and weapon packs to date over the game's half-year lifetime. Yet another email lands in Commander Shepard's inbox, this time asking him to investigate a Cerberus research outpost that's gone mysteriously silent. Taking the recently commissioned Hammerhead hover tank, Shepard and two squadmates of your choosing find the station crawling with geth.

It transpires that a VI at the facility has gone rogue, spreading itself through any available technology and taking over three other Cerberus stations on the same planet (Aite). Even worse, it's trying to transmit itself offplanet in order to spread its homicidal intentions like a virus throughout other systems. You'll drive the Hammerhead between three different stations on Aite in order to access a fourth station that houses the VI. Your squad will need to navigate the stations on foot, with Mass Effect 2's tried-and-true cover-based combat coming strongly into play.

The Hammerhead sections, however, bring some fairly unspectacular vehicular combat into the mix coupled with some interesting (but not terribly taxing) puzzle and platforming elements. In order to reach certain areas you'll need to switch on air vents to give your hover tank increased vertical propulsion. There's even a section where you'll need to hop across rocks floating in a moving molten-lava stream. As you progress, you'll uncover the unsettling story behind the rogue VI; it's a well-delivered subplot that's up there with the best of those on offer in the full game.

It'll take about two hours and there are no new characters introduced, but Overlord presents perhaps the best plot and gameplay variety of any of the Mass Effect 2 DLC packs yet.