I said this elsewhere but I thought R1 was hopeful. That's the whole thing with that movie -- they don't know the message will get out, they don't know they will win, it doesn't matter. They looked at the cost and they said "It's worth it" and did what they wanted to do. With this, it felt....hopeless. Everybody went up against Thanos, repeatedly, and had plans, and the plans fell apart and Thanos just swatted them all aside and at the end he won. It was like if Vader had scooped up the message at the very end.

I also wasn't thrilled with the whole Malthusian thing and "the good of the many outweighs the good of the one" but those were almost incidental compared to how fucking grim it was.