D1's entire story consisted of "Here's some random village you showed up in. Oh, look! A dungeon! Hey, maybe you should keep going down further into it...Oh, look! Diablo! Kill him! Okay, you're done now..."
D2 I didn't play as much as D1, but from what I did play, I can say that the story was just as formulaic. The only difference being that they made the game much larger than D1.
If you want to bash D3's story for not making you feel like you're alone and desperate (yeah, Foo Fighters!), here's a tip: you're not supposed to be alone and desperate. This is now the third time the world has face Diablo, it's the 3rd game with Deckard Cain fighting him in some fashion, the world knows what's up by this point.
To be honest, the whole idea of being some random stranger saving the world is kind of played out. I think they could have made it a little bit darker, sure. But i certainly don't think the graphics look "cartoony", or like everything belongs in Whimsyshire. I think the main reason that the graphics of the predecessors looked so dark was because they were so heavily pixelated in comparison to modern graphics.
Nor do I think the game would have benefited from being as dark as Metro: 2034/Last Light, IMHO.
I couldn't disagree with you more.
While Diablo 1 came out in the days when video games were still nearly exclusively shallow and rather one-dimensional, I think they (Condor / Blizzard North) created a masterpiece for other reasons.
The tone of the narrative, the colour palette, the music, the environment design, and the solitary gameplay which puts you in a very exposed position all blend extremely well. Together, they create a dreary, desolate, gloomy, and hopeless world and gaming experience.
Naturally, D1 and D2 were not as smooth and polished as D3. There are a lot of improvements in D3 as well. But when it comes to the narrative and environmental design, it is very easy to see that the current Blizzard is more inspired by comics, manga / anime, and WoW, than anything else. I'm not bashing those art forms or hobbies, by the way. But I do claim that they do not mix well with what Diablo is supposed to be.
It needs to be influenced by Europe of the Dark Ages and similar sources. That's where we, culturally, best define that mood I'm talking of.
Plus, I don't think the stories of D1 and D2 are bad. Relatively simple - sure. But not bad. They did what they were supposed to do, and aided the environment and world around you in alienating you and putting you on the spot.
It wasn't 'Here's a random hole in some backwater town, go kill Diablo.'
It was 'You are alone, and there is nothing in this world to make you safe or happy - all you can do is stay alive, and try to overcome an unbeatable foe.'
And it isn't the low pixel density in D1 and D2 that made the art so dark. Just look at several modern AARPGs, like Grim Dawn or Path of Exile. They both capture the Diablo feel rather well, albeit with less polish. Diablo 3 does not.