Okay, I progressed forward. I wonder if there's anymore to Metal Gear REX...
First I managed to catch Meryl while she was using the bathroom...although it was actually more like the other way around. Long story short: Snake and Meryl ended up chatting about some deep messages involving how war doesn't create any heroes, and Meryl revealed her silly, sorry excuse for being a soldier. This was also the first time in the game Snake's personality seemed to come into play, and he pretty much confirmed himself as a lone wolf.
Next up, a final confrontation with the freaky Psycho Mantis. Not much needs to be said about this guy that hasn't been said - he's here to toy around with both Snake's and the player's mind, and to provide some memorable fourth-wall breaking dialogue. And I was definitely right about him having a disturbing backstory! Was not disappointed at all by him. His "posthumous" acts of kindness were a good finishing touch.
After navigating through the wolves' territory with quite some difficulty, I happened upon a cutscene where Meryl got horribly injured by Sniper Wolf, with Snake vowing to save her. I ended up looking EVERYWHERE for a sniper rifle after that and I don't have one still. I called the colonel and Otacon afterwards and...apparently it's in the armory below the tank hangar. Great, that place is absolutely crawling with guards.
Will continue tomorrow.