DaS series are action games, of course the action part and level/encounter design is very important. Let's say none of that matters, then what exactly are these games good for?
Unique levels with interesting paths through them. Dark souls 2 excels at creating interesting locations with multiple ways to traverse them in ways Dark souls 1 and 3 don't. Unless an area is an open (probably) swamp then there's basically a single way you can get from A to B unless you unlock a short cut. While the wharf in Dark souls 2 has multiple paths through it with varying risks and rewards. Enemies caring you lit a torch makes the top path pretty safe but no torch makes it more dangerous. The Gutter is excellent for creating a sense of exploration into the deep under world where you have to manage your torch time as you explore. Vendrik's castle has doors you may or may not want to open with little puzzles of where to kill enemies to do it. Heide's tower of flame has challenging enemies gatekeeping making the boss easier or harder. The rat covenant has an immense amount of bullshit to pull you into. The bell ringers and no lights in the Crypt make for a tense experience, especially when you get invaded by NPCs or you run into massive shield guys who refuse to move and have little room to fight them. Compare the Crypt's ghosts attacking you from the walls to the later games ghost hands and see a huge difference in design philosphy. One is a trap you trigger by being too close and the others an invisible hazard spread across multiple areas designed to be annoying rather than something you can react to.
Interesting boss designs. Demon of song is easy but it's an interesting boss to look at with a gimmick played out through the whole shrine. Flexible Sentry is 2 different enemies where you control which you fight. The Ruin Sentinels are a complete panicfest as soon as you realize there's 3 of them and you have to kill 1 on a tiny ledge before the other 2 fuck you up. Nothing in Dark souls 1 or 3 has that same sense of dread. Lost sinner breaking your lock on and NG+ adding an ambush in a boss room. Royal rat vanguard is an interesting take on Fools idol. Cuvetus demon is a push over but a cool design. The poison lake right after makes for an interesting challenge you solve by exploring the level (I won't defend how). The Rotten is an amazing design and is all about space control. If you lose your space the fire kills you and he takes up a lot of room. Smelter demon is an interesting way to pressure enemies with a lot of healing. He will never stop damaging you if you get close to him. Pursurer is a solid boss fight and having him reappear adds a sense of paranoia through out those areas. Guardian dragon is one of the best dragon fights in any From game because it's not just hitting his ankles and hoping he doesn't fly up and roast you and have context for why he doesn't just fly up and roast you as every other dragon should. The Iron king is a huge demon fucker who approaches you and seems over whelming at first.
Dark souls 2's strength is in the quantity of interesting experiences it has to offer. I never used life gems in my first play through and coming back to it I realized they're there because the game isn't about managing your healing resources but it's about exploring a hostile world where healing can't save you. There are plenty of ambushes and instadeath traps in the same way Demon's souls had them. Instead of focusing on 1 v 1 combat with increasingly spastic enemies (Dark souls 3, Bloodborne and Elden Ring) it focuses on being an explorer in a hostile land where most dangerous enemies are swarms of chumps banding together to get a free meal. There's almost no memorable locations in the PS4 era From games because they're all set up to be combat encounters rather than dungeons. I can play better action games with more depth than souls games, but I can't find many modern games that focus on quality exploration. Elden Ring is 70 hours of open world boredom and a few hours of really good dungeons. Demon's souls and Dark souls 2 feel like those legacy dungeons all the way through. I don't cry Heide's tower is misplaced in Majula because I'm too busy enjoying Heide's tower's gameplay and atmosphere to count how many pixels it should be in a background. The volcano castle didn't feel a shocking misplaced location to me despite being at the top of an elevator over Earthen peak because I was excited for the katana knights and explorating the location. My immersion wasn't broken by an unrealistic transition because I was enjoying the content both locations provided and the way you get between those zones is basically irrelevant filler you probably miss because you're taking a sip of your drink any way.
