DS1 had two main issues that persist (well, also Bed of Chaos boss fight was the stupidest encounter in souls history) to the present. First, once you have bonfire travelled in the other games, the long as fuck walkbacks before you get the Lord Vessel are fucking cancerous. The descent down the tree through basalisks is one thing, but you can get the Lord Vessel prior to that. The trip to Nito that HAS to happen prior to the Lord Vessel is completely rage inducing, however. Second issue is some of the boss design is fucking dick punching to certain builds. Four Kings is a good example as it all but requires a full on DPS build to tackle reliably, so GG if you were doing tank. And the dragon "fights" that are basically grind up a stack of 200 arrows and spam the shoot button for 30 minutes are way too abundant. Actually, a lot of the bosses are stupid in various ways (dumb gimmick or specific build needed), but it also has a couple of the most enjoyable boss fights in the series (Spider Chaos Flame boss, Actual Nito Fight is fun and challenging, Big Demon thing in the fire area).
Its still a great game, but aside from the layout of the world its not better than the other entries in the series.
After replaying them, right now Dark Souls 1 is my least-favorite out of all of them.
Demon Souls looks incredibly pretty on PS5 and has a unique atmosphere and world. The PS3 version isn't pretty, but it has an oppressive gloomy darkness that makes it also worth playing. Yeah, I consider the two versions of Demon Souls to be very different from each other.
Dark Souls 2 SOTFS (only version I'd play now) is gorgeous, high-FPS, has an interesting world, has a lot of ways to completely flip the game on its head. Great storyline here with the evil queen and all that.
Bloodborne is the best overall experience even with the terrible FPS, super interesting world and story, weapons that are so good that I still haven't tried most of the ones I want to try, because I stick with one or two for an entire playthrough. Only problem with it is that there isn't more of it.
Elden Ring has the best art direction, looks gorgeous, is sprawling, has nearly limitless things to explore/find, and manages to make those things actually worth exploring and finding because so many of the weapons and relics are useful.
And then we have Dark Souls 1. Technologically rudimentary compared to all the others besides Demon Souls PS3, which had a better atmosphere and fast travel. As for DS1, no fast travel for most of the game, unlike all the others. Some very rough around the edges zones and fights like Blighttown, Demon Ruins, Capra Demon, Bed of Chaos, Tomb of the Giants. The world design however is good and harkens back to the Metroid series. If you look at the world layout of this game you can clearly see how similar it is to, say, Super Metroid. So all of that said, out of the whole series, right now DS1 is the one I find least-enjoyable and have the least desire to ever replay. It's the only one I wouldn't look forward to if someone told me I had to play them all from the beginning again right now. It's still better than most games though.