So I just finished running a session this evening. Fourth session of the campaign, fourth delve into the dungeon. All of the PCs are still 1st level. Red box Basic. All veteran players who have played with me for years and know the game and know my DMing style.
The party went into the dungeon ten strong on this occasion: three PCs (Iowynn the dwarf, Ragnyr the dwarf, Leonard the mage), one NPC (Clara the cleric), and six men-at-arms (Jek, Wäld, Lily, Kurtz, Renée, and Tibbit). Having previously discovered three different entrances to the dungeon, they opted for the south entrance (a secret door behind four towering statues of elvish warriors) because it puts them nearest to kobold territory; on previous delves, they had befriended the kobolds and now counted them as trusted allies. That gave them safe passage through a good number of rooms before they struck out into unexplored territory. They passed through a room occupied by some confused orcs who didn't speak Common (a bit of gesturing allowed the two parties to cautiously avoid each other without a fight breaking out); poked around in some empty halls with broken furniture and statuary; made a second failed foray into a large chamber choked thick with rubble and glistening clear slime, with blind cave-locusts jumping around; but decided on caution and retreated from the big bugs rather than engage them.
Going another way, they bypassed several side-passages and doors, came to a room covered with matted webs, and fought four giant spiders—Wäld was a casualty, but only one dead soldier wasn't going to get the PCs turning around. And they found a cache of 480 electrum coins in a coffer among the webs, just a small treasure but not a terrible take considering the monsters guarding it. In the next chamber, a big grand hall (deserted, with lots of worn statues of armed elves and some furniture crowded around a big stone hearth), the party found some side-passages, but also a secret shaft down to the next level inside the hearth.
And Ragnyr the dwarf (run by my group's consistently most reckless player—he's already lost a character this campaign, press F for Jakob the thief) decides to head down alone. He starts poking around at the bottom, finds a secret door that opens onto a creepy chamber occupied by some mutant sahuagin. And does he close the door? Run? Try to climb back up the rope? Nope. He calls for help from the party and charges, one 1st level dwarf vs. four 2-HD monsters with multiple attacks. So, yeah, in the ensuing mêlée, with the party climbing down the rope one at a freaking time, we have the PCs literally marching into a meat-grinding bottle-neck of their own making, never even considering retreat. Because Ragnyr, the first to fall, was also carrying the bloody treasure.
During the fight, the party lost Ragnyr, Clara, Jek, Kurtz, and Tibbit. Two of the sahuagin were slain, while the other two fled with 1 and 2 hp remaining. Only Iowynn, Renée, Lily, and Leonard made it out of the dungeon—and Leonard never even climbed down the shaft or tried to use his one spell (charm person). Freaking disaster, and it's all because the players made one tactical blunder after another. They could've made out much better if they'd proceeded with due caution and common sense, or used better tactics, or simply retreated early on. But they didn't, and they paid for it in blood.
And at the end of the evening? Laughter and smiles all around. Some weary and accepting smiles, some appropriate pathos for the loss of the NPC soldiers and cleric and the dwarf PC with a coveted Str 18. But the player who lost that dwarf? He just rolled up a new thief with a natural 17 in Dex on 3d6 in order (sacked his Int two points to bump that up to an 18, natch). And maybe he'll play that thief next time, or maybe he'll use one of his other characters (he's already got an elf that survived the third delve into the dungeon and earned a bit of XP for it, as well as a cleric that he hasn't even played yet). The point is, nobody's mad at the game rules or disappointed in how they've allowed things to play out—because everything is fair and above-board. I rolled every die out in the open; and the players are well aware of the fact that their own actions led to the consequences they experienced. They also know full well that better play would have very likely caused things to turn out differently.
And I don't think that they'd want it any other way; because a victory that's been handed to you (whether by a set of rules stacked in your favor or a DM who fudges dice behind the screen to favor whatever you do) is a hollow victory.
Now, what does all this have to do with the topic of the thread? Well, I've seen lots of people ragging on the old rules. Saying that this level of lethality isn't heroic and isn't fun. I'll agree that it's not heroic—of course it isn't, the PCs are only 1st level!—but how could it not be fun? "Disaster sessions" like this are memorable, they're entertaining, and they're also valuable (because the players now know more about the dungeon they're exploring). And while it's true that I'm running this game at home for friends and family who are all old hats at D&D, this campaign is no different from the public tables I typically ran pre-plague. Games which—despite the nigh-inevitability of early disaster sessions, or even full TPKs—never fail to draw in new players. And new players will very quickly acclimate to the very same attitude evinced by my longtime players: a basic understanding that the game is challenging, that the challenge is in a sense "real" (i.e. not some Houdini trick that I'm pulling by fudging dice behind the screen or tweaking monster numbers and hp on-the-fly), and that the PCs' failures and victories alike are come by honestly.
Once you get a taste of that, you can just tell when a DM is handing you a win, and it's not a pleasant feeling. Regardless of whether you're running old-school or OSR or 3e or 5e. That's what I'd argue is no fun and no way to excite new gamers.