Overwatch

I lost my first Retribution game from not everyone getting on the damn ship. >_<

I'll see if I can give some advice while keeping it concise. 

Camping
The most important thing is to make use of the map for cover. Let enemies come to you. Some key locations to camp are:

-The room you spawn in
-The breach after you clear the first room 
-The small library with the staircase (to your left just before you get to the docks); when Enforcers start spawning, it's helpful to stay upstairs
-The building in which the troopers break the door and windows
-The bridge (for the first assassin); have someone trigger the assassin by moving into the square, then retreat back to the bridge
-In the final area, there's a small room with no other exits overlooking the docks (where the boats spawn); you'll need to be careful of enforcers but it provides excellent cover if you don't allow yourselves to be overrun

Enemies
-Troopers may seem weak, but on higher difficulties a small group can burst you down in no time. Try to use cover and peek them when possible. 
-Enforcers close distance quickly and are a one-shot kill at point blank range on Legendary. Keep your distance when possible. If you need to get close, use Wraith Form, Fade, or Deflect to avoid damage. 
-Snipers can lock on to you and are a one-shot kill on Legendary. DO NOT peek them when they are locked on to you; they will stay locked on even if you enter cover, so you'll be greeted with a bullet to the face. Genji can easily kill the sniper with his deflect, and McCree can take her out with quickly with headshots. 
-Assassins seem a lot scarier than they are. McCree's flashbang stuns them long enough for a competent team to burst them down. If they get on top of someone, use a MELEE ATTACK to knock them off. 
-Heavy assaults are the most challenging enemies. You need to kite them in a circle to whittle them down. The area directly behind the FIRST heavy is suitable for this, assuming the Moira is on top of things. In the final battle, you'll need to move in a circuit around the edges of the ENTIRE area. DO NOT bother using ultimates on the heavy assault; they don't do enough damage and are more helpful in clearing trash mobs. 

General Tips
-Don't split up. Doing so makes it difficult for Moira to heal her teammates.
-McCree is the squishiest member of the team. He has the weakest mobility, no way to avoid damage using his abilities, and no way to recover health without Moira. Both McCree and Moira need to keep a close eye on his health pool.
-If someone goes down, draw enemies AWAY from them before going in for the revive.
-Coalescence is probably the best ultimate in this mode. I recommend using it to clear out groups of enforcers quickly. You can also use it on the sniper to melt her, assuming she isn't focused on you.

Hopefully this is helpful. 

Answer me this - why do so many people try to face-tank the Heavy on Legendary? And when they get revived they go and do the exact thing all over again?

Good, that should prevent players from overextending.

Hanzo's new ability worries me - it has a lower cooldown than scatter, seems to be more consistent, and deals a lot of damage. I wonder how people will react once it reaches live...

I went 25-4 as Brigette! And I unlocked the Grounded achievement! I thought I would never unlock it!

Well no one is instalocking her on Xbox anymore, so I can get more playtime with Brigette!

Yeah, some of those achievements you pretty much need the enemy team to try to help you get them. 

First you got her blackwatch skin and now this.... the envy and jealous that I have for you is palpable. 

Hmm, I might have to try that. I usually keep a distance.