Overlord, the latest and largest of the Mass Effect DLC packs, is a mixed bag in the best possible way. It's a medium-sized adventure that never lets one gameplay element dominate for too long, leavening the expected duck-and-cover combat with openworld exploration and a dash of environmental puzzling, all wrapped up in a story that builds to a satisfying and pathos-heavy finale. It is almost exactly what you want from a low-priced downloadable add-on.
It begins, as all these things do, with a new marker added to the Galaxy Map. There you'll find an abandoned Cerberus research facility, dead bodies strewn all over the place and signs of an almighty struggle everywhere you look. Once you discover the chief scientist, conveniently also the lone survivor of the massacre, you start to unravel what went down.
Turns out Cerberus has been researching ways to combine the human mind with that of the Geth. The result turns out to be an adorable little Labrador puppy called Scraps McKenzie, who joins your crew and amuses everyone with his mischievous ways. Actually, no. The result is a murderous Virtual Intelligence that has taken control of all the technology on the planet, and now plans to beam itself into space so it can spread to other worlds. Announcing its presence by howling in an often-incoherent digital roar that is genuinely unnerving, it makes for an effective - if mostly unseen - enemy.
The VI has sealed itself inside a fortress-like underground facility, so your first order of business is visiting two other bases to activate the failsafe protocols that will allow you to take the fight directly to the rogue data packet in question. It's here that the Hammerhead, the hovering tank introduced in the free Firewalker pack, comes into play.
The area available to you isn't massive, sealed off as it is by mountains and gorges, but it's large enough to have a good scoot around without feeling too hemmed in. The Hammerhead responds well to the terrain, with just the right mix of weight and bounciness, and after the sluggish Mako of the original game there's pleasure in simply roaming around, boosting off rocky ramps. The Hammerhead has even gained a deadpan personality of sorts, directing your attention to nearby pleasant views and commenting dryly on the combat data created by shooting the gambolling alien horses with your rockets.
Dotted around the place, there are six Cerberus data packs to find, usually protected by gun turrets that can turn the Hammerhead to scrap in a few seconds. This side-side-quest is really only essential if you're hungry for Gamerscore though, since finding them all triggers one of the two new Achievements (the other is for finishing the story).
It would have been nice to tie these collectables in to the plot, or at least use them to offer some kind of sub-narrative, but they're really a meta-game, there to populate the world a little and justify the Hammerhead's inclusion.
Unfortunately, combat is where the Hammerhead is at its weakest. Literally. With just one mode of attack and flimsy armour, you still end up playing in much the same way as you did in the Mako - strafing wildly, and bunny-hopping to dodge incoming fire.