My kids (10 & 13) and I are wrapping up our first campaign together in D&D 5e, and I'm starting to think about the next one. It's going to be a homebrew setting--future humanity decimated by climate change, but also elements of weird magic with giant plants and insects, inspired by things like Studio Ghibli, Kipo, etc.
After watching the recent Critical Role - Tears of the Kingdom oneshot, I started tinkering with my own system (PbtA based, with lots of opportunities for inventive crafting, and a video-game-inspired skill tree rather than strict classes) which is fun, but really time-consuming.
Wondering if anyone knows of an existing system that would work well for this setting? I'd like to find something simpler than 5e (which is the only system I know well), since they mainly enjoy the story and role-playing rather than lots of number crunching and detailed rules.
Mutants & Masterminds 3e -- available for free online as d20herosrd.com -- can do literally anything. It's originally written for superheroes (obviously), but I've seen it used for D&D style fantasy, sci-fi, and so on. There is literally one single spell in all of fiction and film that I have tried to replicate in that system and not been able to (Balefire, from The Wheel of Time, because weird shit with time). It's all the flexibility of GURPS with a fraction as much math, all the power-fantasy of D&D without the game-breaking power-loops (there are a few but they're easy to spot and avoid). And all the complexity is front-loaded; once you get through character creation, it's all just d20s. If you can play D&D you can play M&M.
For something less crunchy, try Fate. Whether Core or Accelerated or whatever I couldn't tell you -- I personally hate this entire family of systems -- but it is very rules-light and storytelling-focused. It might suit your needs.
Mutants & Masterminds is a neat system, and flexible enough that you can use it to do a lot of different things.
But if someone is asking for a game that is "simpler than 5E", then Mutants & Masterminds would not be my first suggestion. Depending on what you're trying to do, character creation could get pretty detailed.