the whole team has to know what they're doing, and do it at all times. one stupid move like dropping the last ammo bag in an exposed/crossfire position and game over. Even on normal.
Took me around 6 goes with my regular group before we succeeded the first level. A few tactics we found indispensible
- starting positions: two covering the left (one on balcony), two covering right (one in drill room, one in balcony). guard the left flank, specials drop from roof as well. one ammo bag on balcony or top of stairs.
- second holding position: do not hold in the matrix like lobby, hold just in front of the two doors going to vault room. DO NOT FALL BACK to the actual little rooms in the back. Drop ammo in between the two doors, that lets them crossfire you. I can't describe to you how many times I've had public games where people either try to hold in the lobby (and get shot from the sides as they come thru the lifts) or retreat all the way back into the two rooms at the back and get monstered. The two doors is where its at.
- when vault is open, only one guy go in and grab cash, three holds. If only two holds it gets too risky as one guy going for ammo = flank exposed.
Also if the team doesn't have at least the level ups for the decent secondaries (uzi shotgun etc.) its considerably harder. I'd imagine that once you unlock the real tier 2 main weapons (m308, machine gun etc.) it gets a lot easier. I'm still a few unlocks away from that.