Well, well, well.
I'm not usually very attached to games and lists and what have you, but I'm with @DIPSET on this one. This has hit me hard.
Dark Souls is by far one of the best games ever made. Period.
For a start, it's incredibly deep. There are things you won't see in this game for a long time, if not ever, if you don't play it right. Ian of EZA likes to say that the "Form is the Function" a fair bit with this game, and while I do tend to poke fun at his reliance on the phrase, it is so true. The game will never explain gameplay nuances to you, like how to engage in PvP, or how each covenant works, or what you should be doing at any one time. The game doesn't give you lots of exposition apart from the set up at the beginning, and it's up to you to just figure out what to do throughout the entire game, based purely on the wishes of the few friendly NPCs you'll come across along the way.
For example, the Dark Wraith Covenant. On the surface it's just the PvP Invasions Covenant, the game realistically has a vested interest in guiding you towards that mechanic as it's a very unique part of the game that players will likely enjoy. A few Cracked Red Orbs can be found by the player in the game world, allowing them to dabble, but they'll not fully commit without reason due to their finite, consumable nature. They can't relax and enjoy the feature.
But it's practically impossible to join the Dark Wraith covenant unless you know how. For a start, you have to completely ignore one of the very few NPCs that actually seems like a friendly NPC. You then have to, against your instinct, throw yourself in a pit, and then go beat a specific boss. All while still ignoring that NPC that most players will gravitate towards, especially on the first playthrough. Only after having beaten one of the hardest bosses in the game for new players, will you uncover Kaathe, the Dark Wraith Covenant, and unbeknownst to 95% of players, an entirely new way to interpret the main story of the game.
Most people will never have seen that content, and that's incredible. And there are lots of other examples of this, like Ash Lake and the Pyromancers. That elevates Dark Souls closer to a piece of Art than any game I've ever played. Dark Souls has not compromised in its design in order to make sure that Players get to enjoy all the content. It adds up to make Lordran feel like a world that's there to truly explore. Not a Theme Park waiting for me to see all the attractions.
Some might not like what I've described above, but I think that Dark Souls, through Lautrec, a Secondary Character that the game makes you deal with, the game teaches you that you shouldn't trust people just because they're in your safe area and they're not attacking you. By extension, this leads the player to question everything.
The game world is gloriously expansive and intricate. Everything is connected in exceedingly clever ways. For example, many guides will tell you that you need the Master Key to access Blight Towns back door. No you don't. Take the lift down into the Valley of Drakes from the bottom of Dark Root Basin. Run all the way back to the Blighttown back door, grab the key, unlock the door, and boom. You have your shortcut from Firelink Shrine to Quelaag. You can beat the game while never fighting the Taurus Demon too. You can do this easily using the Master Key, or you can drain New Londo in the early game if you're capable, and enter Dark Root Basin and the Undead Church through the back entrance. Undead Burg PvP FOREVER! 🙌
Finally, the online nature of the game was expertly done. From the things that most people will get to use, like the Soapstones, and the Messages, to the things that few will see and fewer will even understand, like the Dragon Covenant, or Vagrants. Even just the bells ringing every time someone beat the Gargoyles. What a great way to make new players feel united in what is likely the first section of the game that most new players will be having difficulty with.
All this is without touching on the normal stuff. The RPG and combat design is wonderful. It's so darn creative, with many different builds and playstyles. There's no single strategy to play the game. You just play to your strengths, and the way you want to play. One of my favourite things about the RPG systems is that you can, and probably should, find a weapon you like and then level it up using the Blacksmith. The normal weapons are the ones that are viable for the endgame, and while there are weapons that give you a short term advantage like the infamous Drakesword, it doesn't scale to end game like the other weapons do. Add in all the special boss weapons and specialty weapons, like the Moonlight Greatsword, the Black Knight Weapons, the Great Sword of Artorias. You could play Dark Souls for weeks and still struggle to obtain every weapon.
Shout out to the Balder Side Sword crew and the Zweihander posse. The Zwei got me to my first Dark Souls completion, and the Balder Side Sword introduced me to the aggressive playstyle that many don't see til Bloodborne.
Finally, the presence of a Souls Level 1 character on the Character creation screen, and the way the game is tuned. I love how more than anything, it's player knowledge and skill that's rewarded in Dark Souls. You can beat the game never levelling up your character. You can leverage the game in such a way that you can one-shot many of the bosses. I know Git Gud is a meme at this point. But in Dark Souls, that sentiment is always true. If you persevere, if you learn the game, watch that attack pattern, figure out your moveset on your favourite weapon, there is nothing the game can throw at you that you can't overcome. And that's amazing.
I think this is the biggest post I've ever written on this forum. I love Dark Souls. It's one of my favourite games of all time, and has shaped the way I look at games today. The top 3, from my best guess, are all well deserved places. One in particular I'm really happy has placed so high.
To finish it off, here's an old video from vegeta311, where he challenges himself to one-shot as many Dark Souls bosses as possible.