Enough not to dismiss preference for an old approach as "just nostalgia."System matters. The question is, how much?
Sure: it's limited to categorizing system!Are Necromancer Games 3e adventures and Goodman Games Dungeon Crawl Classics part of the old school renaissance? If yes, then that shows the limitation of system as a means of categorisation.
NG and GG have published new editions of old material, and GG has published the Random Esoteric Creature Generator. GG at least has also published scenarios that in their linearity are the antithesis of OS -- which was true of some classic TSR tournament modules as well!
One could say that, but one would be wrong. "What the game was like before 3E" is pretty much the operative definition of OS. The big issues with 2E are not to do with the core rules.One could even say 3e itself was part of the old school renaissance with its 'Back to the Dungeon' after the more setting and story focused 2e.
That's dubious, and in any case the game as a whole manages to make 3E look good by comparison, from an OS perspective.One could also say 4e is old school in several respects.
There's a coat of "d20 system paint" in ascending AC and the "SIEGE system" (which is not really a system at all, but provides an illusion that may comfort some). What's underneath is pretty OS. Some folks have "history" with it from development that left a bad taste in their mouths, because it had been billed as a new AD&D. It's not AD&D.And yet sites such as Grognardia or Dragonsfoot seem to be very anti-d20. But Castles & Crusades is widely recognised as being both d20 *and* old school.
There may be a problem you have chosen to make for yourself, but that's easily solved by letting the OSR speak for itself.So there's a definite problem in defining what is and isn't part of the old school renaissance.