Basically every break down of the fourth wall in Metal Gear Solid series leaves me both chuckling gleefully and scratching my head and feeling my brain get sucked into itself. "Because the internal feed mechanism is shaped like an infinity symbol." "Yep. That'll give you infinite ammo, alright!" WHAT?! WHAT?! WHAT?!
The fake-out credits in Shadows of the Damned. I did not see that coming. Oh, and while on Suda51, the very concept of Killer7.
The entirety of Deadly Premonition, specifically in regards to the facial expressions and character animations. Oh my god, the fact the game was even released is just mindblowing. It really is pure entertainment. Everything about it... Jesus. So fucking insane.
Oh yes, and some of the later moments of FEZ (starting with the fake OS reboot), that very much implies that you are controlling a character who basically exists inside a NES cartridge. And then of course the game expects you to start translating a language, and I had to whip out pen and paper. THAT was a big "what" moment. It also made me grin with delight, because I realized how much hidden depth there was to the game. But yeah, just the whole atmosphere of that game goes from delightfully retro to 16-bit hell over the course of a few hours. Definitely blew my mind.