Indie rpgs: Annoyingly specific rules.
OSR: Annoyingly specific content.

Unpacked: There are hardly any limits on what Indie rpgs do. From staging a play about familial estrangement (My Daughter, The Queen of France) to wooing a knight-errant (Kagematsu) to finding out the true names of city-people and city-things (i'm sorry did you say street magic).

But to get people there, you have to be annoyingly specific. No play culture or handed down mode of play like adventure gaming will do this. To the extent that Kagematsu exhorts the reader to "set aside assumptions you may have about role-playing games."

People throw their hands up about this in frustration: I don't want new rules systems, I want content. I can't with designers forcing people to play a certain way. If I can't plug it into the game I'm running at my table, it's useless to me. And so on. They're right in a way.

The old school on the other hand is wide open for content. Everyone can (blog-)post a place, a monster, a class, a skill-list for other people to put into their games. A published module like Dead Planet will tell you in its very first sentence to "cannibalize it. Rip it apart."

But for that, you do need shared assumptions about how roleplaying games work and any content will be annoyingly specific to them. To the common idea of how people and characters will interact with the morsels cannibalized from blogposts or module. Enter The Adventure Game.

Escaping from this gravity well is so difficult that OSR content is sparse even in well established adventure rpg genres like Science Fiction or Horror. This has started to change recently but from an Indie perspective, it's all frustratingly limiting still.