A fantastic concept with an enormous capacity for world-building!
The closest I can come comparing it to anything else is by describing it as a Metroidvania Little Big Planet. There *is* a story mode, but the user-created maps are the big draw, in my opinion. To date, there are over 2,000 individual stages, each with their own unique charm and difficulty.
You can build and play parkour challenges, combat stages, or story-driven puzzles. You can create pixel art. Make it easy, make it difficult, make it funny, sad, or scary. The possibilities are endless.
Each user's level connects to at least one other, depending on how they set up their entrances/exits. Sure, gaining access to a particularly interesting-looking stage can pose an issue if a connecting level is ridiculously difficult, but a good deal of the time, you can either just find an alternate route, or even build your own connection!
I hope this game gets more attention as time goes on, because I think it's woefully underrated. I've put nearly 40 hours into it so far, and I haven't even explored a quarter of what's there. An astounding amount of content for a 2D platformer, and the number of map squares yet to be filled in with user content is absolutely bonkers. Hundreds upon hundreds of thousands. I'm not kidding.
You could literally claim a huge block of map squares somewhere far away from anyone else's world, and build your own full-on platformer, complete with dialogue, traps, monsters, and any other bells and whistles your heart desires.
Awesome, awesome game. ^w^