DnD will always be the monster, as said. I couldn't stand it after 3e/3.5e, which turned me off so badly that I can't possibly look at DnD again without nausea. There's a reason why people LOVE DnD, but I can't stand the new stuff to the point it hurts to look at it. It's like an intense feeling of betrayal, it's so visceral. I can't fucking stand it, but that's on me. DnD is, and always will be, the ultimate gateway drug into the universe of tabletop RPGs.
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FREE LEAGUE has been hitting it out of the park with their Year Zero engine, IMO, adapting it to old school (Twilight 2000 4e) and newer games alike. Is it overly complex? No, although Twilight 2k is very crunchy due to its old school/wargame lineage.
IMO, the ALIEN RPG is maybe one of the finest adaptations of a license, and even with the Cepheus/Hostile (Traveler 2d6 system) being great at the same head space, ALIEN is such a tight experience that it's a shame not to recommend that one. It's not going to be uber popular compared to the likes of DnD, but everyone knows FREE LEAGUE is quality stuff and will have at least heard of what's going on. Their boxed starter sets are borderline perfection when it comes to starters, and the books are beautiful. They're just amongst the best in the business right now in terms of quality - both in terms of production and game content.
ALIEN is just plain tight. Twilight 2000 has a lot of shit to track, while ALIEN is so much more refined. I can't wait for the Space Truckers book & the Colonists book to flesh out those modes of play (like the Colonial Marines Ops manual), and the next cinematic scenario should be very good at a minimum. (I find both Chariot of the Gods & Destroyer of Worlds to be quite good, though not perfect.)
(FREE LEAGUE's The One Ring, which is an adaptation/update of the 1e TOR rules, is also one of the finest licensed products you will ever read. It's the perfect distillation of the Tolkien experience this side of the Burning Wheel, which is indecipherable to many people... so you'd have to look at The One Ring for a Tolkien-style game that you can pick up and play, but it's a much more niche audience than DnD.)
Modiphius & 2d20 is also up there, but I find their books to be a little difficult to read. Star Trek was really difficult, anyway, and that should have been a home run due to the license. The DUNE RPG is incredibly easier to read, but the lack of practical examples of the structure of play really hurts this one... and boils it all down to the usual/traditional, "Go to Arrakis, do dumb stuff, kill things & take their stuff" DUNE campaign. I think they have a winning system, but it's hampered by their inability to get out of their own way with it. Too much woke, too many conflicting ideas, not enough clarity in what I've seen.
Apocalypse engine/PbtA is pretty popular as well, although it is a minefield of wokeness. Games like "Masks" and "Dungeon World" are really high up there. The KULT 4e reboot is not as woke by far... it's horror/strangeness, almost like a TOOL album in game format, I think. The system is not very hard, but KULT is a harder interpretation of PbtA to hang onto unless you are disciplined about what goes onto the character sheets (so you don't have to flip through the book). You really need to master the flow of it and have a high trust environment with the players to deliver the "TOOL album in game format", however. PbtA games are a high wire act at the best of times, and at the worst of times? Can be aimless and insipid.