I also didn't shoot any of those people who hanged Lugo, I just shot the ground, but then later in an audio log, Walker says he killed those people to restore order or something, but I didn't actually shoot any of them
I read some comments about the gameplay being generic with swarms of soldiers and heavy music on purpose in some sort of criticism of military shooters, but I'm not sure that's true. I would think that if they wanted to mock other shooters they should have done something like in reality Walker has been captured by US forces for war crimes and in his head he is defeating all the 33rd whom he blames for his actions. Then one of his captors could ask him if 3 guys could really kill a whole battalion.
I will see if I can watch the other 3 endings I read about on Wikipedia.