Plenty of lucas arts adventure games to consider grim fandango being one of them. Stuff like Loom, the original monkey island, monkey island 2, day of the tentacle, the dig are worth searching for.
other point and click adventures like beneath a steel sky and the broken sword series are worth snapping up. The former is also free, so no reason to not play it.
Oh and the rise of CD meant being buried full of actors in front of green screens. So stuff like The 7th guest, ripper, black dahlia will be on the list.
i suppose commandos, doom 2 (although more for the community wads) and unreal tournament (the rival of quake 3 at the time).
if we're counting the 90s as it 1990 -2000 we might be here for quite a while....
i could probably list the older stuff that probably hasn't aged well that were brilliant games for its time. Like moonstone : a hard days knight or normality, the original worms , dungeon keeper, dungeon master, rise of the triad etc etc