Manguard flowchart: Charge>Biotic ARM!>Shotgun>Repeat
I saw a video of a Vanguard utterly slaughtering TiM's troops with a vanguard. The guy was a fucking cross-between comet and Hulk. A later posted detailed how to do it:
Take the talent at the end of the Charge tree that lets you recharge shields 100% whenever you charge. Take the Nova talent that reduces the Charge cooldown by 25% each time you Nova. Put some more points into making Nova awesome (this guy opted for the "Novas have a chance of not reducing your shield" talent, but it doesn't really matter which ones you pick). Run with a light weapon to keep your cooldowns as low as possible (this goes for any character as far as I'm concerned. The only reason I'd ever equip a second weapon is if I were playing a class without a damage power on Gold, where ammo starts to become an issue).
Once you do this, you stop playing a third person shooter and start playing Hulk in space. Your Charge and Nova talents will recharge as fast as you can trigger them, and your shields will reset constantly. It can be risky on Silver if you run into too large a group, and you have to be even more cautious on Gold. But it's still ridiculously fun.