Steal da Choppa
Played this mission on my own so some comments aren't true in your case as you recommanded four players for this mission.
Briefing
I suggest putting in links in the briefing to markers on the map. As it is now I didn't have a clue about where to do stuff after taking the chopper - luckily the waypoints showed me where to go. Uhm you might want to check the spelling of the briefing. The briefing is okay, I think that it could've been written a bit cleared though. With additional information on a seperate page or in the notes section.
Weapon selection: M4 ACOG + Launcher, 6 HE Grenades, M9 pistol with two magazines, M136 + two rockets, two hand grenades and four magazines.
Mission
Crossing the bridge with my team is possible, but they are a bit slow to do so. But it's something that's not too important for a coop so nevermind. Anyway, I engage the enemy soldiers patrolling the area and succeed in getting a visual on the chopper without too much trouble. That's good as the difficulty shouldn't be too high, at least not for this part. Anyway, I try to move closer towards the chopper and take out two more enemy soldiers more or less guarding the chopper. As two of my three teammates refuse to get in the chopper I'm like whatever so I let them run towards the other side of the island. They don't make it, I can tell you that.
The other guy gets in as gunner, a bit useless as he's an AI but he probably took out one guy during the take-off, couldn't see didn't bother checking. I flew towards the little town in the north, forgot its name, and the first time I got shot at and died after taking too many rounds - probably one in a lethal position. After reloading (saved about halfway towards the town) I put the chopper down earlier and got out with #3 moving in column formation towards the occupied town. Immediatly we came across a few patrols, heavy skirmishes took place and I had to reload numerous times, had been stuck on a reload (1 minute after landing the chopper) for about 20 minutes - that really pissed me off, hehe. My problem though, shouldn't have saved in such a dangerous position.
Anyway, clearing the town proved to be more trial and error than I'd hoped for. So for me the difficulty, or here number of enemies could be lowered. Because not only did it prove to be trial and error, my pc also lagged a bit. But this depends on the player, one likes to have numerous shootouts, I like a realistic battle. After killing the officer and most of the guy left in town I decided that it was enough. I don't know if I had to clear all of the enemy units as the objectives didn't get completed upon killing the officer and I was not in the mood to go hunting for that remaining soldier.
Overall
The start was good, the second part wasn't too enjoyable for me. Two important drawbacks, the numerous enemies and the objectives not getting ticked off? Anyway, stealing the chopper was nice. With three human teammates it would've been better, with good coordination etc etc..