There have been many times that I was impressed with the graphics of a game, but few that I recall absolutely blowing me away.
1. Sonic the Hedgehog (Mega Drive), after playing C64 and NES games I couldn't believe a game could look so good with all that parallax giving a sense of an actual 3D world stretching into the distance.
2. Donkey Kong Country (SNES) This looked like it was on a different console generation to me at the time. The graphics were detailed and almost looked like 3D models, I was ready for graphics to reach perfection (or close to it) with the Ultra 64 until....
3. Virtua Fighter 2 (Saturn) I vividly remember watching Shun Di stumble about as shots of other fighters cut in all while the camera moved about in full 3D (something that Tekken 3 copied quite well) and completely forgetting that I was expecting Toy Story graphics on next gen. I fully embraced this 3D wonder with it's detailed character models and fluid animation. I think the frame rate was a huge part of it, though I didn't recognise that at the time.
4. Shenmue (Dreamcast) Playing Shenmue at release was special and made me feel like the Dreamcast was going to stand up to the PS2 and later consoles from Nintendo and Microsoft. Putting aside the gameplay, the graphics had such a high level of detail, the textures seemed like they'd been ripped from photos of real objects and locations. There were such a lot of objects cluttering the streets and the interiors of buildings. Ryo's facial detail seemed like it could have only been some kind of tech demo, not just one part of a game, one I could actually play. The future was now (or then) and if games could look this good then I couldn't imagine how they'd look on the next gen consoles. I did notice some glaring flaws such as how NPCs often just had block hands with painted on lines for fingers, while Ryo had well modelled hands (at least in closeups), but overall I was awestruck by the attention to detail in the world.
5. Gran Turismo 3 A-Spec (PS2) Now I was getting my perfect CG graphics. The TV ad just showed a car sitting and looking at the sunset in one of the courses and my mind was made up, I was going to buy that game and a PS2 (I was going to get a PS2 anyway but I thought it would be later). I got the game and played it for countless hours, sure I could see some of the shortcomings such as reflections not always matching the trackside banners) but I actually enjoyed the game as well as being bowled over by the graphics. I'd played Metropolis Street Racer on DC and thought that looked nice and it was cool to see real life cities in a game, but GT3 just looked so much better. Once again, 60fps was an important part of making it look so good and this time I realised that.
6. Uncharted 2 (PS3) The early 360 and PS3 games looked nice to me (including Uncharted 1) but they didn't really blow me away. That changed with Uncharted 2, I first saw it in the official UK PS mag where it obviously got about 500 pages dedicated to it's E3 showing. It looked incredible in screenshots but it was when I actually played the game that I was floored. Everything looked so much better in motion, the depth of field effect when aiming seemed like some kind of magic, the animation was mind blowing and the textures and effects were eye popping (like the DKC boxes always used to say).
7. Horizon Zero Dawn (PS4) This might be the best looking game of all time in my opinion. I'm impressed that an open world game can look so damn good. Not the last game I have been impressed by but the last one to truly take me by surprise with how good it looked.