This is interesting, let me throw my choices and suggestions in. (For the record, most of these is based only on viewing the gameplay of others through Youtube)
1: I'm surprised there's no VR/AR (virtual reality/augmented reality) categories in the list, because most of the time those, Sandbox and Action-Adventure Open-World games are my favourite in order and I would have thought immersion would be unequalled in VR's case so I would have suggested:
H3VR (Hot Dogs, Horseshoes And Hand Grenades VR), Blade And Sorcery, Hard Bullet, Pavlov, Onward, etc regarding VR, Garry's Mod regarding Sandbox, and Sleeping Dogs and Elden Ring regarding Action-Adventure Open-World, mods for these games are insane (particularly Blade And Sorcery, GMod and Elden Ring, and I think H3VR as well)
2: I agree with God Of War Ragnarok and God Of War itself, but Elden Ring in my opinion purely due to variety and scale is above Sekiro, not even counting the mods on top of that, I'm not sure whether I'd put Assassin's Creed Syndicate/Unity higher up but ehh still happy to see it in the list
3: Tekken, Dead Or Alive, Soulcalibur etc should be up there in Action Fighting-Duel (The 3D aspect really makes the fighting that much more complex and "realistic"/immersive in terms of freedom of motion, not to mention the combination of striking, grappling, weapons and supernatural abilities) while Smash Bros Ultimate should be in Platform
4: NO WEB GAMES?
Firstly:
A community effort to preserve games and animations from the web.
flashpointarchive.org
This exists if you want to relive Unity, Java, Shockwave, Flash, and other disabled plugin games, so there you go.
Additionally:
i make shtuff for curious & playful peeps
ncase.me
If you like educational and also fun games.
Secondly, I'm pretty damn sure Nitrome (they're remaking their games so they requested Flashpoint not to archive said games), Miniclip (before it went to crap with layout design and before game choices crashing down in number due to plugins), NotDoppler, AddictingGames, Armour Games, Kongregate, Y8, Box10, Stickpage, Newgrounds, Cartoon Network, Nickelodeon, History Channel, BBC, etc made our childhoods (for those of us old enough to know about them before NPAPI plugins were unsupported)
POWDER GAME, SUPER BRAWL, STICK WAR, GUN GAME, 300, 1066, SIERRA 7, PLAZMA BURST 2, DEADSWITCH 3 (yes it's on Steam but DAMN IT), DRAGON FIST 3, WARLORDS, LEARN TO FLY, RAGE, JELLY BATTLE, WARRIORS, JURASSIC FIGHT CLUB TURF WARS, CARBON COMBAT, WARMERISE, XIAO XIAO, THE LIST GOES ON NEAR-ETERNALLY!
(I'm not actually mad but I am surprised these were not added at all)
Hope you agree with these suggestions.