You may be interested in reading my Mass Effect 2 combat Guide, for more general information.
There’s not much to say about this one really. Rather than facing off against a tough enemy such as the gunship, in this boss battle the mass effect 2 designers decided to have you fight legions of Vorcha. It’s not too tricky, but if you’re having problems I can give you a few pointers that should guide you through the waves.
Firstly, there are a LOT of Vorcha in this boss battle. Don’t leave cover until you know they are all dead. When you turn a corner, assume there’s going to be more Vorcha behind it- take cover and look from safety!
When you use powers, focus them all on one target. The Vorcha’s insane regeneration skills mean that unless you finish one off in one salvo- he’ll be back at full health in seconds. If you have incendiary rounds by this point, use them to help with taking care of the regeneration factor. Heavy weapon Vorcha are of course, your main target for this boss fight.
Go for the head. Vorcha have very little HP, even if they do regenerate like crazy, so a couple of shots to the head should be all it takes. If you are playing a soldier, the adrenaline rush is great for this. If you have biotic powers, use lift to make them easier targets for your team mates.
Some krogan are thrown in with the Vorcha waves to give this boss fight a little variety. All in all, when they appear you should give them higher priority over the Vorcha as they take longer to kill, and come at you with shotguns.
Try to take down as many Vorcha as possible from the raised central section before processing down the aisles of the arena. Their numbers will be replaced, but thinning them out from relative safety helps a great deal. If you can, switch to a sniper rifle to do this.
While this isn’t really a boss fight, I’ve written this guide anyway. It is a challenge at the end of the level, so don’t expect it to be easy. Just take your time, and this bit I can’t stress enough- don’t leave cover unless you know everything is dead. Don’t turn a corner without using corner peak first. If you do this, then this ‘boss fight’ is easy.