Just to see what game made you last stand back and say "Wow."
There are very few games out there that not only have good graphics, but they actually blow you away.
I remember probably the first game I ever saw which made me do that was Turok 2 on the N64. Not a very good game, and I often wished nothing more than to meet the level designer so I could beat him to a pulp, but damn it had some sweet visuals and plenty of OTT gore. The next game that stepped up to the challenge was Soul Calibur on the Dreamcast, I remember just sitting there for about 5 minutes just watching the game. The next one was GT3, I remember seeing the previews of the replays and I was just blown away, it looked so realistic, and it still does.

The most recent game which has made me reassess what I think is good isn't Half Life 2, nor Doom 3, but a humble little offering from Relic (I think) called Dawn of War, which is based off the Warhammer 40,000 franchise. I remember the other game FireWarrior was total crap but Dawn of War is just something else as far as graphics go, just because of the sheer scale of detail on it. You can have about 30 or 40 units on screen battling it out among each other and the animation and detail is fantastic, especially when you zoom in on the action and pan the camera across. My main regret about the game (and so many RTS's) is the lack of a Dungeon Keeper style possession ability to fully take advantage of showing off these awesome visuals, but I suppose you can't have everything.

So what do you guys think of which games not only have good graphics, but excellent graphics?