Invisible Sun is the most satisfying game I've ever played
... and it's not even close.
It requires a stupid amount of buy-in from the players.
They need to read one manual for character options, another for how magic works, and then maybe a chapter from a third one to understand how to actually play the game. (The GM has at least four manuals to read, so of course the scale is still tipped the right way.)
In the first session, players help shape the world, but not in a big universe-spanning-all-encompassing way. They create their own tiny neighbourhood. The setting is potentially huge, but these characters are just regular people vislae1 with jobs, houses and a flair for the uncanny. They can tell you about their regular 9 to 5, their favourite shop and maybe that old lady who lives with the pigeons and bakes mean blueberry tarts.
The character options are so many it takes dedicated players ages to actually sift through them all. Most just pick whatever strikes their fancy first. And there's so much to catch your imagination! Every time my players need to pick something new to develop their character I'm super envious helpful because I can't wait for them to try something different and amazing at the table.
With all this, you know you're getting someone who's not only dedicated, but especially excited to play and show off their character. And players care so hard about their house and neighbours it's silly how easy it is to have them dive into plots.
Magic and spells work for the GM, not against them.
One of my players got a spell2 that lets them see the future. As soon as it was picked, I internally groaned. I'm very forgetful and I do almost no prep for my games, so having someone constantly asking "what's going to happen" already spelled disaster in my head.
But I love it. Per the spell, the character is shown an event involving a person that they know, but, most importantly: the event unfolds as seen "if I and those I know do not intervene in any way." It's absolutely perfect! It's a very slight "GM please help me out", but it leaves everyone freedom to do absolutely anything else. This is how divination spells should be handled.
Funnily enough, the first time this spell was used, everything happened exactly as forseen. The players completely forgot about the vision after about one hour of play, but then acted it out exactly. As soon as I pointed it out by telling the seer "You feel a shiver down your neck" everyone's mind was blown. Definitely a highlight of my GM career.
Ideas are everywhere.
Reading nine manuals (yes hi I went overboard), some of them multiple times, was absolutely not a chore. Weird secrets are scattered throughout. Every other paragraph holds prompts that could span brief encounters or entire adventures. I regret not writing down every single idea I got just by reading the manuals, but I still got plenty. Definitely more than I can use in one year of play.
The Invisible Sun setting, taken as a whole, is absolutely huge. It would feel daunting, if it didn't go exactly the right amount into detail. People, places and organisations aren't written as an encyclopedia to be studied: they're alive with issues and relationships. Secrets are hinted at and maybe hidden in a tiny paragraph in another book.
I'd never used a premade setting before. I remember, as a player, trying to read about D&D 3.5's Eberron, or Dark Heresy's Warhammer 40k. They felt so dead, useless, boring. You'd either memorise a bunch of facts, or completely forget what the hell it was all about. When I started GMing I vowed to stay as far as possible from premade settings. I have now read The Path3 back to back at least four times.
It's physically huge.
There's so many pieces, cards, maps, handouts, bits and bobs. The 14 kg (YEP. FOURTEEN.) Black Cube is a chore to move, empty and then put together every time. But how beautiful is the table with those weird-sized character sheets, my stupid round sooth deck, the Path of Suns board with the Testament of Suns on top!
It made me put effort into making physical prompts, something I had barely done in my life as a GM. It made me buy keys and journals and maybe soon coins and gems to give my players. And anything I make for them, every object they hold, well, it just draws us in more. We're hooked.