DArt, with all due respect, talking about a game that you played only superficially (that is, like 10 hours from 120 hours + game) results in things you are saying being not true at all.
The upgrade system is exactly what you say you like: small and large changes at the same time. The attribute system takes baby steps that over a longer period make up huge changes for your character, partly by unlocking gear requirements or giving you boosts on mains, like health, stamina, damage, etc.
The large changes are gear upgrades, and, finding gear in the first place. This is not Diablo where gear is poured on your head 24/7. You can miss stuff. You WILL miss stuff. And all the stuff is valuable for one build or the other. All of it. There are no useless items in the game (maybe a few fun items or easter eggs), they are maybe just not for the type of character you are building, or not for the level range you are in. And since all the non-generic items (like longsword) have ONE single iteration per playthrough, and since high-end upgrade materials are very very rare, each and every upgrade has final consequences. You really got to put thought into what to use and how. It's not just damage increasing somewhat, it's stat-dependencies changing, damage type changing, etc.
Add to that the fact that there are no two weapons that share the exact same move-set. And in this game, move-sets are everything. Different move sets are good for different encounters. And it's not obscure either. If a boss has long hands, you gotta have something with better reach. If - and here's where lore ties in - the guy is a demon, you should try lightning damage, since lightning was wielded by the gods, their enemies. If the boss shoots huge blue magic orbs at you, you should give a shot to Magic Barrier or armor with high magic res. If you feel you are slow, try lighter armor. And you gotta be changing stuff around, exploring and obtaining. Because if you don't, you will die. Encounters will not go down due to attrition. Everything is more durable than you, since you are a human, a weakling in the beginning, and you are challenging the powers that be.
There's also no two players preferring the same weapons or move sets, and everyone finds their own style, only to later discover how other styles work really well, too. I've had full caster, full melee (DEX), Dex-Caster, Strenght-armor builds, and all of them are viable (and these are not all of them, by far). Classes are pretty similar in the beginning (except some have better gear and better foundations for certain builds), and you need not follow the class build.
Around level 25, characters look and play very different. Mid game they are vastly different. They can choose from different equipment, have completely different spells and moves, you feel it's a whole new aspect of the game. And what is genius is, that all of them are useful (and not in the "Diablo 3 skills are all useful but make no difference and feel no different" kind of way…).
As for the areas, the initial one does feel a lot like Demon's Souls, but beyond that it's more diverse, larger, and quite different. You get forests, lava lakes in caverns, the city of the gods, crystal structures, a pitch black cemetery, a flooded city, etc. I loved Demon's Souls areas, and Dark Souls gives more variations. I would not call it dark and bleak (especially since the first areas are sun-drenched and teeming), but more like, murky and rotting away. The world is ending. You are fighting the long defeat. But that doesn't make it worthless, since in the end, you get to decide the fate of all creation. And by that time, it somehow matters to you.
A sense of history is very much there, and you can delve into it deep. I have seen few games that inspired so much valuable fan theory and speculation - in a good way. The game is full of intriguing symbolism and commentary on humans and human nature. How the best of intentions can turn out a disaster if power is wielded without responsibility. If we meddle with things we do not understand. I think you'd like it.
I also get the Diablo 1 comparison you made, but I don't agree with all of it. I never felt for a single moment I had to do any pattern learning or skill-based gameplay on the scale of the Souls games in Dio1. I had to click click and then see if the loot dropped is a small upgrade to the King's Sword of Haste I have. At level up I put most points into the most important attribute for my class, out of 4. Occasionally I got uniques that were good but not great.
I don't mean to offend, or educate, but I thought there should be info from someone who actually played the game to bits and pieces.
Edit: Sorry for the wall of text.