Animal Crossing: New Horizons

Just kidding!

I heard the game got a second wind and did alright.  I didn't play it till a year after release, and what a fantastic game that was, from start to finish. This game deserves a sequel

It's predecessor, Vampire: The Masquerade - Redemption had it even worse, getting totally squished between Deus Ex and Diablo 2, two games that are still very fondly remembered to this day and had massive hype upon release while V:TM-R is mostly forgotten outside of fans despite being an absolutely great game and story.

Advance Wars also doesn't seem to catch a break in this regard: The first one released September 10 2001 - and I don't think I have to tell you what happened the very next day - and it's remake got delayed because of a war, resulting in that one getting pretty much shadow-dropped and forgotten on the shelves. Though I wonder if Advance wars had a scheduled release any later than it did if it even still would have released at all in the west...

Propeller Arena. Never officially released. The game leaked tho and has been our for many years unofficially. It's a fun combat arena game where you fly around in a plane and battle friends. The problem with the game is that it was planned for the fall of 2001. One stage takes place in a city with skyscrapers, and it is possible to crash into them. The game was cancelled only a couple of days after 9/11.

DriveClub.

The game released at a time the review industry was quite hostile to non open world games and released just a week after Forza Horizon 2. Plus the GAAS model of DriveClub was too early, now it's normal to release games piecemeal, same as season passes.

Motorstorm Apocalypse had the bad luck to have a planned release just a week after the 2011 Earthquake and Tsunami. It was delayed in many places out of respect for the victims and was badly tainted by association. It was the end of the series.

Battleborn releasing in the same month as Overwatch 2016.

Metal Gear Solid 2 is the obvious example for me, it came out at 2001 with themes that are extremely relevant today, and received a newfound appreciation in the MGS fanbase in recent years. It also helps that MGS4 made Raiden cool.
I almost want to say Tears of the Kingdom came out too early too. Could you imagine if it was a Switch 2 launch title, with all the S2 Edition improvements out of the gate?

For games that are late, there are so many, but I want to say that, as much as I enjoyed AC Shadows, "Assassin's Creed Japan" came out 10 years too late.

Warhawk (PS3)

Socom Confrontation

MAG (Massive Action Game)

Home

All games from Sony's online only multiplayer push during the PS3 era. They were all a gen too early. Their GAAS wasn't nearly as controversial then.

Lego The Hobbit: Released many months before the third movie and never got content from it. The game seems to have been profitable but could have sold more and gotten better reception if it was a complete story.
Cyberpunk 2077: Released in an unfinished state. Things have worked out in the long run, but it was a baffling choice.
Marvel's Midnight Suns: The stench of Avengers was still hurting Marvel games, plus Midnight Suns is an obscure team making any timing challenging.
Sonic Superstars: It released 3 days before Super Mario Bros. Wonder and Spider-Man 2. Who was playing Sonic that week or talking about it?