Played Platinum today. Made it to wave 7. Me and another group member carried the whole group who had abysmal scores, I don't think they noticed it was platinum match. I was demolisher and she was Fury. And yes, it was public game. So I guess we made it pretty far considering. On wave 7 everyone had died except for me which forced me to run all over the place with lots of geth and reapers around. It was Banshee's warp dot that finally made me in.

The new shotgun has really wide spread, it's extremely close range auto-shotgun. But very good at what it does. Unfortunately didn't unlock the new assault fifle either. I agree with Matth regards to the new pistol. I doesn't fire at all unless charged up, which makes it very unintuitive to use. It's beast against shields and barriers though, but only tickles armor and health. So it's basically made for adepts whose biotics have difficulties against strong shields.
Unlocked all characters. I really like Fury and Demolisher. I could watch the new adept's ass all day long.

The destroyer is pretty nice soldier, too bad the shoulder missile launcher is really weak considering it drops your shields to half. Which when used with devastator mode which makes you slower and unable to dodge, is bad combination. I had pretty good success with the Paladin too, cryo, incinerate and energy drain makes for really versatile class. And the shield allows you to take cover and regen shields even when under fire, at least until it receives too much damage and breaks. There are some attacks that apparently can instantly break the shield, I'd be especially vary of phantoms and any particularly strong weapons like those of Atlas and Prime. For some odd reason it also seemed as if geth hunter's plasma shotgun might have bypassed the shield sometimes. As far as I know, the shield doesn't protect against sync kills, so don't bother bunkering down when facing a banshee.
Shadow and Slayer really aren't my cup of tea. Then again, vanguards in general aren't and I'm not usually running infiltrators either. With the exception of Krysae wielding Salarian engineer when farming geth in FB White. Krysae equipped with disruptor ammo and energy drain make nice tech bursts and cloak provides nice damage boost to the Krysae.
The new maps have some serious glitches though. There are some parts where you and mooks can fall through the map. I saw it happen even to an Atlas. Thankfully it re-appeared when it moved a bit. Vancouver also has one ladder where you get stuck for a moment every single time when you use it to go down. Bioware also messed up unlocking some of the weapon mods, only half were actually unlocked and the ones there weren't working have even been removed from the multiplayer manifest. No idea when BW will fix the issue and add them back.
The new wave goal is to escort a drone from one point to another. The drone cannot be destroyed but it has a radius in which at least one team member must be at all times for the drone to move. The more team members escorting, the faster it moves. However, escorting can be real pain in the ass when it happens to go through an open area, allowing mooks to practically fire at you from other side of the map. I'm guessing infiltrators would excel at this job by escorting while cloaked (with duration specced cloak) and then taking cover while cloak recharges. This must be particularly brutal in platinum difficulty. Imagine this goal popping up at wave 10 in a map that has plenty of open space.
Now, where the hell is that new patch? There's crapload of small bugs that needs fixing.