I played 1 through 3, including a bit of Resurrected. I definitely favour 2, though, having played it for probably thousands of hours.
I'd recommend any of them, 2 even more so, what's with the release of Resurrected.
Diablo 1 has an almost old-school D&D feel to it, establishing many staples of the series, such as the itemization, the lore, the character stats and inventory management aspects, among others. It definitely feels a bit dated, but I'd recommend trying out DevilutionX (on GitHub) to mitigate that. It's a project that adds many quality of life features and allows the game to feel a bit more of a modern experience, with larger resolutions, better and configurable controls, access to content that was cut from the original, and many other things.
Diablo 3 is the one I played the least, but I'd still say to give it a go. It's more of an arcade experience, with combos, hordes of enemies, giant numbers on wearable loot and, as much as I could gather, a simpler experience all around. It's probably the most hated entry on the series, but I still had loads of fun with it if only for lore reasons.
Diablo 2 is… well, Diablo 2. Depending on whether you play LoD ("Classic", you could say), or Resurrected, it can be a very unbalanced game. Builds and classes are clearly better than others. Itemization is on its own level, being the best I've encountered in my entire life and the main reason why I keep coming back to it. It's also why it's such a grind of a game, which is not for everyone. Anyway, I definitely recommend 2 over the others, which is not to say that they are not good games.
As for plot… well, you can play all games without reading a single line of dialogue, but you can if you want and I like the games for that.
Edit for clarity: you don't need to play the games in any order, as the plots are mostly self contained, but I do think it's very rewarding to go through them and seeing the plot unfold. There are many iconic moments.
I’ll throw my vote for Diablo 3. The game can be wicked addictive. I got the platinum trophy on PlayStation which was no quick feat. I just couldn’t stop playing. I would suggest choosing the Crusader to play as first. Super fun and has these flails that are specific weapons to his character. I had so much fun with the Akkhan armor set and the legendary flail called Fate of the Fell. Can take you well into the torment difficulty levels. Chef’s kiss of a game. I think people should really give it a chance if they like the Diablo style of game at all.
I wouldn't recommend going as far back as the first one. Diablo 2 Resurrected came out last year and is a good starting point for the series if you're thinking about trying it out. I never got into 3, but so far 4 feels really good.
You have to remember that this game came out a long time ago, it had many features at the time that set it above other games.
It had a good storyline, multiplayer, maps that would change every time you logged in (multiplayer), the ability to be powerful after spending a lot of time in the game (and if you saw anyone with a rare/cool looking armor you know they worked for it, there were no lootbox mechanics where you could just pay money for it). And of course... there is no cow level ;)
The skill tree allowed for tons of different abilities and combos, or you could grind away at a single skill and become godly with it.
You may not recognize the appeal to the game now just because so many of the mechanics have been copied and implemented in countless other games since then.
As a warning, this game is wildly complex. I played up to the first boss and kept getting wiped immediately even though I would handle the mobs in the area.
PoE is a fantastic game but for beginners learning builds and stuff can be challenging, if you aren't afrai of guides or just want to piddle around without one for free you can really learn what the Diablo series is like.
Having sunk tons of time into D3, I can say it's worth a look. The paragon leveling system from D3/D4 is a clever way of rewarding players who keep playing well after the main 3 (or 4 with D3 DLC) acts. I think I was at Paragon level 1100 or so when I stopped playing.
The biggest complaint people had about D3 IIRC was it's too colorful (something they poked fun at with the Whimsydale/rainbow goblin).
D2 was a favorite in college, but admittedly I never played outside of some lab parties.
D4 is shaping up to be a solid game, but this is patient gamers, so I don't know if that counts.
Oh no, how dare a game known for its dark visuals make use of the whole spectrum lol. If that's the highest critique then it's gotta be the best dungeon crawler of all time
Yeah, but they aren't fun if you run into cheaters. They're a blast if you play with some of your friends. There are other similar games too, so I recommend you give the whole genre a shot.