I’ll compare some of my main observations.

Environment: Dark souls 3 has incredibly cluttered environments in a good way. Every room has stuff in it, corpses and furniture and little details that make it feel alive, claustrophobic and horrifying. Compare that to ds2. So many rooms are just empty, empty boxes with nothing in them. This significantly changes the atmosphere of the game and once you notice ds2 is just empty rooms you can’t unnotice it.

Combat: Actually ds2 was pretty good except for hit boxes. But ds3 borrowed most of the good changes from ds2 anyway and dropped the (imo) bad ones like healing stones. The bad part of ds2 combat was definitely soul memory, an absolutely horrible mechanic for longevity of pvp in non designated pvp zones.

Vibe: already talked about this a bit in environment, but ds2 feels like a Skyrim adventure. It isn’t scary. Hollows are just zombies and there’s never any really scary moments or eldritch creatures, it feels sanitized almost. Ds3 had a lot more eldritch horror and that helped complete the vibe.

Bosses: so many of the bosses in ds2 are just bad or cut and paste. So many. Both rat fights are dumb, cut and paste dragon riders, so many fights are just “big knight with big weapon”. All the best fights are either the end of the game or the dlc. Contrast that to ds3 where the bosses are challenging but fair and have much more polished themes, more varied movesets, more lore, and are just in general more fun. The only truly bad ds3 boss fights imo are the one dragon that gets one shotted and wolnir.

Enemies: the game design philosophy of ds2 is just “put tons of enemies with huge lock on ranges everywhere”. Much less polished than ds3 and it feels artificially difficult. This was somewhat fixed in sotfs but not enough.

These are just some of the reasons, I could probably list a few more.

Just gonna interject with Jacob Geller’s DS3 video https://invidious.snopyta.org/watch?v=lnAWQz34PJs

The first half of Dark Souls is one of the best games ever made. The 2nd half is unironically worse than Code “bro look off of a cliff and find a hidden path lmao” Vein. In this way, I think DS2 is a truer sequel to DS1. Incredibly high highs, unbelievable lows. DS3 oftentimes feels too polished - if that makes sense. Weird and offputting is necessary for these games to work. Not to say DS3 is bad, but it doesn’t really feel as rotten (positive connotation) as I think it sometimes wants to.

Bloodborne is the true superior sequel to DS1 because it actually represents a leap forward in both mechanical and aesthetic design. Nasty game, love it.

Dark Souls 2 was a you-had-to-be-there-at-launch situation. It was an entirely different experience of a game when there was no meta. I spent days in the royal rat covenant sewer area pvping, i was the rat king of the sewers, farting out poisons. There were these crazy builds you could make like invisible giant club, 1 ammo one-hit-kill go for broke magic build (i think the spell was called hex?), poison farts, and a fuggin ben hur horse boss lmao. It also had a very unique aesthetic and I liked the story as a cautionary tale about marriage. Places like Heide’s Tower of Flame felt like fully realized dream landscapes, almost Daliesque in a way. In terms of lore its my favorite cause of Aldia and his content, he really elevated the series. There’s also a giant dragon the size of a building that’s hard as hell. Dark Souls 3 just felt like it wasn’t trying to do anything and I barely remember any of it. The most fun online pvp I’ve had in a Fromsoft game was Dark Souls 2 cause of the whacky builds. It’s like the Temple of Doom of the franchise and I like that.

I wish I could articulate Dark Souls 2’s aesthetic and vibe but it’s hard to put into words.

Dark Souls III has a more consistent level quality of content that seems to prevent it from ever sinking to the level of something like Bed of Chaos or Frigid Outskirts.