Man, how about Killer Instinct. When this game was in the arcades it was amazing to watch. Even more amazing was the "Ultra 64" promo that was on every arcade unit for this game. It had all of us thinking games were going to look that good on the U64.
The moment I saw Alucard dashing thru the courtyard, cape flowing in the wind, then jumping the drawbridge, I KNEW this game was gonna be something special!
I remember being impressed by all the little things going on in SoTN. The fairy familiar would rest on Alucard's shoulder if he stopped walking, and then would make a falling off motion when he moved. The way Alucard handled the nunchuks looks very well done. The shimmer of the invisibility cloak was my favorite little thing though. That just looked so damn cool.
This was probably the last game to truly blow me away graphically. And it was also a very BROWN game. Don't underestimate the power of brown motherfuckers. 
I honestly find this game more graphically impressive than RE5, which to me lacks any originality or inspiration in its art....I mean its got Gears of War gloss mixed with a shooter war setting like everything else. And even though there have been some beautiful games obviously on the HD consoles, there's not much that stands out. RE4 though.....wow, I remember going through the game for the 1st time in early 2005 and just inspecting the detail in every room, just like I did for Metroid Prime in 2002. It took me double the amount of time it should have to finish the game because of that.
It was a wonderful showcase for what we should have had much more of on the Gamecube.
Banjo Kazooie was an absolutely amazing looking game in 1998. This game probably blew me away more than any other N64 game...it was so far beyond anything at that time really. One of my favorite games ever....it was like a sequel to Mario 64 that was bigger and much more beautiful, and I loved the vibe and humor of the game.
Shenmue was pretty impressive.
So was Soul Calibur...
Still one of the most amazing intros ever. My jaw was on my fucking lap.
The only time brown was cool in gaming.