Walkers are attracted to movement and sound. When the group stopped and were talking, they should have had walkers attracted to their voices. The zombie clothes may have confused the walkers as to where they were at first but the walkers should have started congregating towards the group. After continuing to talk the camo should have failed (which it did for Sam and Jesse).

Fire has both sound and movement. The walkers at the front who could see the live prey would not (and did not if I remember correctly) turn away. It was the walkers rows back that didn't have a good sight of prey that the light, sound and movement of the fire pulled away.

Lighting the lake on fire gets the walkers away from the buildings and into the lake. If they are submerged then sound won't attract them. Getting the walkers into the lake doesn't end the problem however. Now you have a lake full of walkers since fire does not kill walkers.

Glenn was lucky, yes. I think they wanted it to seem that Sasha and Abraham were were firing down the wall so Glenn was less likely to be hit but the camera angles didn't mesh - Abraham and Sasha were not firing parallel to the wall but perpendicular. But I think they messed that up.

They also messed up Maggie's predicament. Enid was able to scamper up the wall then walk along the wall to Maggie's platform. Maggie should have been able to walk down the wall herself instead of staying on a swaying platform. Also she could have went over the wall and dropped down.

Lastly, they should have killed off more people in the showdown. No way a few didn't get overwhelmed by walkers or just unable to handle hand to hand with walkers.