Dark Souls
Like a lot of people, I'd make it to the Capra Demon and decide I had no time for DS1. Which I still think is a fair decision to make. There are other ways to spend your limited time.
The notable thing about that fight isn't that it's hard, though, it's that it forces you to come to terms with how Dark Souls works. For a long time I thought these games were 3D Castlevania, but despite sitting within a lineage that includes a certain kind of 80s action-adventure game, your Castlevanias 2 and Rygars and Battles of Olympus, that's not exactly it. Dark Souls is 3D Donkey Kong, or take your pick of one-screen arcade puzzle platformer. It's about reading the room and determining where to put your feet. People compare it to a rhythm game; I'd say instead that it's a play except you don't know your part and have to either learn it from context or improvise. I realized I wasn't thinking about how to beat the Capra Demon or the dogs, I was thinking about how to beat the entire room, blocking out the whole performance of the fight in my head, and my first attempt at it afterward was a win.
I have to risk sounding combative or self-congratulatory here by saying that most people who like these games don't know how to articulate what's good about them. Or at least most pitches haven't done a great job of selling them to me. The idea that they're all about manual skill and the RPG stuff is secondary is totally false--you can treat DS1 like a build-making numbers game if you want, and engaging with all the systems it gives you for upgrading weapons etc. makes progressing through it much easier. Talking up the item descriptions as great writing seems extremely goofy from my perspective as a lore-hater, but there is sometimes clever storytelling happening in the way DS1 presents information, and the setting works very effectively as an interconnected gameworld. I've also been unfair re: how brown and gray it looks given that this stops being as true outside the starting areas. It's grim, I guess, but funnier and more cartoonish than you might assume, which for me is a massive point in its favor. There are some excellent nasty little freaks in there, even if some are not strictly little.
DS1 is in some ways, or at times, a triumph of design in which all the formally disparate elements that constitute a game work toward a unified effect. It's also janky well beyond the level that its reputation for tight design would lead you to expect. Enemies can attack you through walls or while facing the opposite direction, sometimes due to clear intent but often not; with certain weapons you can attack them through walls back. The idea of fighting rooms isn't always well-executed, particularly in the back third or so, when things start to fall apart a little. While dropping souls on death is a very minor punishment for failure, the inconsistent checkpointing and long death runs are the one real criticism you've probably heard about the game even if not paying much attention to it.
Basically it's an 8/10 game with the reputation of a 10/10 game. But I say this as someone who thinks 8/10 games are often more interesting conceptually and better able to target people's aesthetic strike zones than 10/10 games. Dark Souls isn't compelling because it's a flawless work of genius, it's compelling because it commits as hard as it does to some of its weirder elements. The thing that makes it interesting as a case study in game design is that it made a very strong argument for the enduring relevance of fairly narrow, curated experiences at a time when everybody was thinking about big open worlds and procgen, about two months before both Skyrim and the 1.0 release of Minecraft. It comes closest of any non-indie game I've played to recapturing the feeling of mystery in all those NES games that mainly got there through weird translations or lack of space on the cartridge for very much text to begin with.