My problem with IWBTG isn't the difficulty, but the fact that it seems built to punish instead of teach.
I enjoy high difficulty games, for example, I've beaten Megaman 10 with the Mr. Perfect achievement, earned shiny golds on all of Donkey Kong Country Returns time trials, and completed every level in Super Meat Boy. I've played the original IWBTG up to defeating Mike Tyson, but it was a tedious, grueling journey to do so and I didn't really enjoy it.
The unfair deaths aren't the only thing - Syoban Action did those, but because most of them were relatively easy to avoid if you knew what you were doing, they weren't so troublesome. IWBTG not only pits you against unfair deaths, but even when you know it's there you still have to make some absolutely precise jumps to avoid it. That razor thin precision combined with long sequences of obstacles that need to be cleared to reach another save point are what creates artificial difficulty and makes the game unpleasant to me. On top of that, a recurring theme is that once you do master a difficult jump, the game immediately follows with another cheap death, and makes you replay the last segment again before you can start to master the next obstacle.
If somebody created exactly the same game, but made it so that each unfair death only occurred exactly once and then didn't impact the player again, the result would be much, much better received than IWBTG but boast all the same high-end difficulty. This gives the player a chance to see the levels and get experienced before coming back to master the game on a subsequent play. Providing a gradual curve of difficulty over multiple plays lets you ramp up to the same end difficulty level, but teaches the player more effectively.
I think IWBTG a good game design philosophy with the high level of detail in each obstacle, and the myriad of surprises it packs between save points. Where IWBTG falls flat is it refuses to teach the player how to play and survive before it demands perfection.
I think this is a good comment, but I'm not sure if it would pan out as simply as you predict! For one, how is long segments of performance "artificial difficulty", while say, a surprise spike is not? I think a funny thing here is that I also have a number of people who make fun of the game for being nothing but memorization -- like, as if all you need to do is memorize things to win, with no element on performance. People don't like that! Now, I'd love to see a game that teaches more or takes a different approach to the whole thing -- there is a lot of design space going on her -- but I'm not sure it would be, given equal quality, a better or more popular game. Any game of this style is to a degree going to be inaccessible, so if you're already trying to appeal to hardcore players, is easing up and cheapening the difficulty going to help? This reminds me of this interesting pricing anomaly. You'd thing "Cheaper the price, the more you sell", but we know that higher prices can infer a sense of quality or prestige or even legitimacy that can INCREASE sales. IWBTG's nature creates a lot of chatter. The fact that the game is considered to be "the hardest game ever made" (which is clearly not even close to true) does a ton when it comes to attracting the target audience. You also get a trade off. A lot of IWBTG's brutality is an illusion. I often make things that look harder than they are. They both fill you with despair but make beating them seem all the sweeter. Being more "teachy" forgoes that advantage. It's not without it's benefits (more people get to see more of the content), but it might not produce the same type of ravenous fans or get into peoples heads the same way.
Now to talk about Gaiden, I THINK (and we'll see over time if this worked) what benefited it a lot was the grappling hook. It's fun on a very basic level to swing around and it requires and allows for bigger, more open spaces while still maintaining challenge. It makes skill tests more satisfying too. Even though navigating things in IWBTG are REAL skill tests, navigating pixels with a character that has perfect movement (in the sense that he has no momentum or air limitations. Not that my controls are PERFECT or something arrogant like that) isn't necessarily as fun. So despite the Grapple arm's bugginess (which should eventually be fixed!), Gaiden apparently feels a lot more enjoyable for players. Now, I think my sense of presentation and timing have improved after all these years and that's also helped, but I think the hook helped a ton.
Though like I said, there is a lot of design space here, so all it takes is someone who feels comfortable in that space to make a great game and it can be a lot of different ways and succeed. I'd be glad to be proven wrong and get totally blown up by some amazing project though! That's what I was expecting from Abobo's and was really excited about it, but it couldn't keep the gameplay quality as high as the art/presentation quality. Thanks for the comment though! Unlike a lot of stuff here, it was actually very thoughtful!
I'd just like to say that despite my dislike of this series, Kayin earns major brownie points for actually responding to criticisms in such a badass manner. If you ever make a game that's easier/dumbed down/casual, I will play it out of respect.
Thanks! I hope you like Castlevania then! Or more so, Castlevania with some sane difficulty options.