I'm depressed that 90% of the posts here are all "zomg teh grafix!!1!1!".
No wonder gaming is so stale, stagnant, and "safe" now.
Ah, it should be expected, but the way you put it make it sound so dramatic.
It's not because we first think about a graphics-related jaw-dropping moment that it would automatically mean that we don't have gameplay-related ones and suddenly '"gaming is so stale, stagnant and "safe"', please.
I myself posted here with such a "zomg ze grafix!" moment (Crysis, sunset at the beach scenery). But I also agree with you, there's not enough thought put into jaw-dropping moments when it comes to actual game-play. I have some in mind right now, such as the first time I saw Half-Life 2 in action back in 2003 during the game's reveal at that year's E3 Expo. I do think I literally had my mouth open and was speechless when I first saw that demonstration of materials and physics interactions, with the breaking effects (wood that breaks like wood, glass that breaks like glass, etc).
And what to say about my reaction when I first saw that famous facial animation and expression demo when they showed the G-Man talking. It was mind-blowing, and not so much about graphics (although the facial textures on the G-Man, at the time, were already impressive). And, again, in the game itself when I played it and first got my hands on the physics gun I then understood how important the game was on a technical level for the gaming industry in general (bringing physics to such a level and quality in gaming).
That, or I could mention my jaw-drop moment when Mass Effect 1's credits started to roll on screen, which is when I became speechless as I was trying to process the epic journey I had experienced for a week until that point. The culmination of every single aspect of a well-crafted game coming together to form one of the best games I had ever played in my life, and only realized it fully when it ended. I literally stared at the screen and watched the full credits without really being there at all, I was kind of mind = blown and just thought for myself "BioWare you guys did it again, you freaking did it again!".
That or... the above but apply it to Dragon Age: Origins.
I'd have many others, but to me a good game-play related jaw-dropping moment can be just as good and important as a graphics-related one. With this said, however, I have to say that the frequency of such moments (be it in relation to graphics or game-play) just keeps lowering as the years pass, but it still happens every now and then. And the LAST time I genuinely had my mind blow when it comes to graphics truly was the first Crysis, it was just a quantum leap as much as Half-Life 2 was (and arguably the original Far Cry as well, but I still preferred Half-Life 2's more photo-realistic approach combined with clearly superior animations and facial expressions, and of course, story).