My journey:AD&D is closer to B/X than 5e, IMO. However, I'm also fairly certain a determined DM can make anything work. But if you are looking for a particular feel/style and you don't use the native rules, I believe it will always feel off (long term).
I spent about five years running 5E with an old-school spin (e.g. AD&D-inspired Magic Resistance that could negate spells like Wall of Force and Conjure Elemental instead of just giving you advantage on saving-throw-if-any; much slower natural healing; damage is not capped when you reach zero HP and if your HP goes below negative [your max HP] you die). I invented rules where necessary to make interaction modes besides combat entertaining, e.g. establishing trade routes, running for sheriff of the refugee space colony you established after accidentally destroying your home kingdom, building a fearsome reputation as a gladiator by defeating other well-regarded gladiators (high reputation is not the same thing as high-level). I invented multiclassing rules that let you be a classical fighter/mage, while still not being obviously better than a 5E-style Fighter N/Wizard M or a straight Wizard. (Each has its pros and cons and playtesting revealed that players perceived a real opportunity cost to either choice, which is good.) I used WEGO initiative instead of IGOUGO to encourage player cooperation and ward off the dreaded Not-My-Turn Player Disengagement Syndrome that afflicts so many 5E games.
But it was a lot of work, and I still had to deal with lots of 5Eisms that just didn't seem idiomatic to change but also didn't have a solid grounding in game logic. For example, why do I have to teach new players that "you can cast two spells on the same turn if you Action Surge, but not if you Quicken one of them because you can't cast a bonus action spell and a non-cantrip spell on the same turn." And why can a Lore Bard use his mouth to recite verbal components to cast a spell "as an action" on the same round he is using a flute as his spell focus for material spell components as part of the same action *and* giving an inspiring speech to one of his comrades via Bardic Inspiration "as a bonus action" *and* denigrate his enemies to impede their performance via Cutting Words "as a reaction"? How many mouths does this Bard have exactly? Honestly this never came up in play, but the fact that if it had I would have had to shrug helplessly and point to the rulebook while saying "It didn't seem fair to you to change it," that bothered me. WotC writes rules in game jargon and with a combat-centric focus ("as a bonus action [during combat] you can inspire...") instead of in-character ("before a battle you can make a short speech to inspire..."), and while in some cases an appropriate fig leaf can be found, other times it's just an ongoing challenge to suspension of disbelief.
And then there's stuff like teaching new players how Concentration works (note: AD&D has concentration mechanics where it makes sense for specific spells, but they are self-explanatory) or that you only get one bonus action per round, and the horrible exploitable mess that is the mounted combat rules.
And then I started remembering how much I enjoy things like AD&D priestly spheres that make a priest of Oghma feel different from a Christian Cleric or a priestess of Idun, and thri-kreen and half-giants that are actually very different from humans both in cultural and RP terms and also in mechanical terms.
And I started losing my desire to run old-school 5E instead of just running a TSR variant. And shortly after that (within a year), my last 5E campaign ended. I'm still interested in 5E as a platform for CRPGs and DM tools (my current project, https://maxwilson.github.io/ShiningSword/, supports both AD&D and 5E) but I may never run 5E again as a TTRPG. But I'm increasingly feeling ready to run my close friends through OSR or AD&D modules like we were kids again, but with greater sophistication that comes from age.
So that's my experience. You *can* do old-school adventures using 5E, and it works okay, but eventually you start asking yourself why you're using 5E as a base and there's not a good answer.
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