I've had lengthy times where I grew tired of D&D and wanted a break from fantasy, which then led to me running other game systems in different genres such as Mothership, Call of Cthulhu, Savage Worlds and so forth. More recently I have been facing a stranger issue: a desire to run something D&D-like, just NOT actual D&D. I mean, I am running and enjoying D&D....but I know it is less because of the current edition rules at this point than it is because of the campaign I am running, and the sundry plots and characters; the game is succeeding despite itself, not because of itself. Indeed, I realize that my main problem with D&D 5.5 (2024 edition) is that it's frankly just more of the same....lots of noteworthy changes, but none of them shake it up mechanically beyond being a horde of slight iterations. It is like they patched D&D 5E, and you notice the improvements, but ultimately also notice its still just the same game. To run with a video game analogy: they added in ray tracing an patched a loot exploit so it looks cooler and plays more smoothly, but its still the same game you've already played to death.
This has gotten me looking in to other options for a fantasy fix which mix up the mechanics sufficiently that I can feel a breath of fresh air even if I am still running some archetypal adventuring campaigns. I've explored Tales of the Valiant and while I am eager to test it out as a GM, it's still got the same problem D&D 5.5 does; it's just a variant on the thing we've been playing for the last ten years already. Pathfinder 2E Remastered is also good at "D&D like" so it's a bit closer to what I want....but in many ways it is the closest direct competitor to D&D, and has its own unique range of issues when it comes to applying it to classic D&D-ish fantasy without being D&D.
This leads me to a few other systems I've considered, as follows:
Mythras Classic Fantasy - this just recently received a huge upgrade with the new Mythras Classic Fantasy Unearthed expansion. If you don't know what this is, it's a hack of the Mythras Fantasy RPG (which is itself a valid alternate to D&D) in which it retools the game's chassis to accomodate classes and a very "D&D like" level structure, along with a D&D-derived magic system and plenty of monsters and magic items. It is Mythras at core, but reframes everything to feel like D&D. Specifically it feels like an emulation of AD&D 1st edition, just now powered by a BRP-derived game engine with lots of skills, D100 mechanics and an extra heap of lethality. Cool stuff.
Pros: Classic Fantasy is a very robust reimagining of D&D style play in a more gritty chassis powered by Mythras; it is well supported with a bunch of modules, main books, the Classic Fantasy Imperative (a ORC-license restatement of the rules as a stand along product, though note you will still want the original Classic Fantasy book for Mythras as it holds all the monsters and more goodies), and the new CF Unearthed book. Plus, you can use all the other Mythras material with it, it's fully compatible.
Cons: I always run into a stumbling block with Classic Fantasy, which evokes for me two things: AD&D and Mythras. I then leave myself wondering if this mix of chocolate and peanut butter really work, or if it makes more sense for me to simply play straight Mythras or straight AD&D. I also prefer BRP Itself, over Mythras, another issue entirely. Also, the special attack rules for Mythras can lead to player decision paralysis, a very common issue I encounter when running Mythras.
Fantasy Age 2E: Green Ronin quietly released Fantasy Age 2nd Edition last year and I am not sure anyone noticed. It's since released a Cthulhu Mythos and Technofantasy expansion on Drivethrurpg, and the 2nd edition is largely backwards compatible with prior books. Fantasy Age, if you did not know, is derived from the Adventure Game Engine (AGE), originally created for the Dragon Age RPG, and this is a full-on iteration designed for use in whatever setting you want. It is class and skill based (though they use focus and talent terms), and is in many ways similar in structural design to D&D with leveling up, escalating hit points and lots of fast paced, hard hitting magic. The latest edition is more robust than the 1st edition Basic Book, too.
Pros: You get a similar experience to D&D but will find Fantasy AGE allows for a lot of design flexibility; its a great system to make unique looking characters, and is pretty easy to GM as well. It has ample support material and the core book is pretty robust.
Cons: Some people find the high starting hit points take getting used to; combats will last longer, sometimes when you don't expect them to. The stunt system unique to Fantasy AGE can lead to a bit of decision paralysis for players, but I find that a few sessions will get them very used to it. Also, because its core design was meant to emulate a video game, it can sometimes feel a tad video-gamish.
Cypher System - Godforsaken and Others: Cypher System has had a lot of expansion into the realm of fantasy gaming in the last several years. The Revised Cypher System rules have plenty of content, but if you add Godforsaken and the Cypher Bestiary you have all you need for a robust D&D-ish campaign but powered by the deceptively simple point-pool system of Cypher. They also have the Planebreaker setting, a new Diamond Throne update and the Ptolus City Setting out for Cypher, most of which were originally settings for D&D 3rd edition or later 5th edition, so its got support for D&D-like campaigns baked in.
Pros: Cypher System is a resource pool game system with player-facing die mechanics which is incredibly easy for the GM to run, and you can simultaneously make very archetypcal D&D-themed characters and also go as off the rails in PC design as the GM is willing to let you. It de-emphasizes a lot of the nitty gritty mechanical elements of D&D, but with the cost advantage of making story and collaborative engagement top priority.
Cons: Cypher System, despite being so cool, can be hard for classic RPG enthusiasts to wrap their heads around, as the pool resource mechanic is counterintuitive to more simulationist rules systems like D&D. Cypher System also works best for GMs (and players) who enjoy improvisation and ad hoc developments, and the game really shines when this is leaned into, but flounders badly if you rgroup does not embrace it.
There are some other ones to consider too! In brief:
Basic Roleplaying, Runequest and Magic World: BRP has a nice new edition update out, and it just got a GM's screen. It's plus is BRP is the best system ever, but its downside is they don't have a single unique modern resource for providing fantasy gaming content. The core book has some material, but its not robust enough. A few years ago before Chaosium changed ownership they published Magic World, which does do exactly that, but its only available in PDF and POD (and had a lot of errata). It's not a bad option, but it is a shame that BRP's latest edition does not have more setting/genre resources out for it, and it continues to get neglected in favor of Runequest. Runequest, in turn, is a great alternative to D&D if you want to really experience something different in the world of Glorantha, but a difficult setting for most to parse out and make their own. If you just want a system to power your own creation, Runequest will disappoint.
Dragonbane: This is a hybrid reimagining of what the original BRP Magic World of the 80's (from the Worlds of Wonder Boxed Set) became in Sweden, also called Drakar och Demoner, and it was brought back with a Free League flourish, now based on a D20 mechanic instead of a D100 mechanic. It's actually a really neat alternative to OSR D&D gaming, but it needs a bit more support to serve as a broader tool set for enterprising gamers. It also has a problem of looking and feeling like a D&D alternative, but in fact being much closer to its BRP roots and therefore being rather deadly to any game group which plays it like a straight up D&D dungeon crawl. I'm keen on trying this one out eventually, but it's not going to scratch the "D&D but not D&D" itch for me.
Savage Worlds Fantasy and Savage Pathfinder: actually these would work pretty danged well for scratching the "totally D&D feel but not D&D at all" itch. Pathfinder for Savage Worlds brings in classes and themes modeled from Pathfinder 1st edition and is not so wed to Golarion that you can't hack it for your own thing. Add in the SW Fantasy Companion (revised for SWADE) and you have essentially all you need to do everything I've been talking about. The top reason it might not be as ideal is because Savage Worlds excels at being multigenre, and I have found that I enjoy it a lot more in a modern or SF setting than fantasy....though that said, Savage Pathfinder rocks hard. The other problem with Savage Worlds is if you associate hit point bloat and long, protracted combats with the D&D experience, then Savage Worlds may not work for you! It's too fast.
There are others I have not mentioned....GURPS Dungeon Fantasy and the reissue of The Fantasy Trip both come to mind, for example.
One of my game nights needs a change of system soon. I think it's probably going to be Pathfinder for Savage Worlds, but I might talk them in to a short campaign in Dragonbane just to see how it feels. I am super keen on Fantasy AGE at some point as well, but I really want to absorb the nuances of the system to feel comfortable with it, first....and that requires time I rarely have these days!