I'll go a little retro, since I find the subject fascinating and most of the time the delays meant the game came out very different than originally intended.
Legacy of Kain : Soul Reaver (August 1999)
Was originally supposed to come out around late 1998, got delayed and design changed massively. Technical masterpiece for PS1, not only did it pull off a big world by streaming all the data constantly, it also ran at a higher res
The Dig (November 1995)
Development began in 1989(!), game changed engines and design philosophies multiple times. One of those games that tried to do away with SCUMM and eventually ended up using it. By the time it came out it was still really beautiful, marred only by the fact that it did not offer an SVGA mode.
Thief (late 1998)
Originally an Action/RPG title where you had to fight Merlin's forces, was to come out some time in 1997. When it came out it was not the most graphically advanced game, however it did offer Software and Hardware Acceleration, looked the part and most importantly hit the nail in the head with the sound design. Thief pioneered a lot of positional audio tricks without any hardware assistance (although I believe it supported A3D?) that to this day a lot of games struggle with.
Dungeon Keeper (June 1997)
Famously late to the party, was initially supposed to come out in 1995. By 1997 it still looked really good though, Bullfrog got a lot of mileage out of that Magic Carpet engine.
Half-Life (November 1998)
Was initially supposed to come out in 1997, but they ended up reworking it massively. A look at footage or media from 1997 reveals that the game was very, very different. Graphically, there were arguably far more advanced games by the time it came out, such as Unreal of course, however Half-Life pulled off normal environments instead of medieval fantasy settings or futuristic bases, so it was really appealing.
Ultima IX (late 1999)
Another famously delayed title. Initially started life as a software rendered isometric game in 1995-1996, but eventually ended up being a 3rd person game with hardware acceleration mandatory. Notoriously buggy, insanely demanding, but it looked pretty damn good back then.
Outcast (Summer 1999)
This is an odd one. Outcast began life around 1995 as a grand action/adventure game, but at the time the fastest CPU was a Pentium 133 and 3D acceleration was not a thing just yet. As such, devs developed an engine that made heavy usage of voxels to render vast distances. This was phenomenal at the time, but by the time it came out Outcast was both amazingly impressive and also somewhat underwhelming. Because it was a CPU rendered only affair, it had to run at low resolutions (maximum 512x384 !) to keep performance steady, but software rendering allowed them to pull off some amazing feats such as vast landscapes and water ripples and reflections among many other things (Anti-Aliasing, convincing DoF effects, beautiful particle system etc).
If anyone's interested to learn more, I wrote a lengthy review on this game's remake that came out last year since I adore it so much and I went to some length to explain the technical matters as well:
https://ragequit.gr/reviews/item/outcast-second-contact-pc-review-english/
I'll be sure to post more as they come to mind.