Vanguards are pretty over powered in bronze matches. Even in the later waves, they just need to be a bit more careful. Sometimes it's just not a good idea to Nova right after a charge as you loose most of your shield when you do. I have a level 19 vanguard. I've had matches end after the first round because the host quit when I killed everything before team even fired a shot. I've been kicked out after a match several times too. I try not to be too assholish about it, I go for objectives, rush to revive people and stay in the zones for the hack nodes, occasionally charging out for a needed shield boost or if there's a large group of enemies near by. I've also learned my lesson the first time I charged a mech/banshee (you get one-shoted with no option to revive).
The class is pretty buggy though. There's a frequent bug where you can't fire off your abilities for a 1-2 seconds, which is can spell out a death sentence depending on your luck. I've also charged through geometry and got stuck outside the map several times. Unless your nearly finished the match, you might as well quit if that happens. Enemies can still shoot at you but you get instantly revived when you die, so If your entire team dies and it's not a objective based round it becomes impossible to finish the match.
I would probably play a different class if I had a weapon I liked to use. I've just been unlocking characters and appearance options every time I buy the veteran pack. I'm only missing the Drell vanguard and Asari adept at this point.