There has been a lot of talk on what this tiny little thing of ours actually means.
I'll throw my hat in the or give my $2 (inflation and all that) and suggest what I think it is.
#2 Reclaiming Imagination. Older forms of the game relied very much on the players and DM's imagination, sometimes to a degree where even mediocre support material was a relief. It was ideas you didn't have to come up with. What I think some of us are seeing is that the newer games (like 4e say) are so systematized and structured that they are a child' puzzle rather than a toolbox for adults. All the flavor is provided and while that has its upsides (fast prep with lower work) its sucks some of the joy out it.
#3 Reclaiming Ownership . The older less rules intensive systems belonged to the group more than anything else. More than just a few house rules it was a sense that this was "Your Groups D&D" not "the 3.5 rules"
#4 Reclaiming Judgment. Matt Finch in The Quick Old School Primer calls this "Rulings not rules" but that implies a bit more of an adversarial "I wear the Viking Hat" relationship than I like. Judgment is simply relying on your own calls,both as GM and as player "why not try that" Modern games seem overly systematized for that style of play and for some thats a detriment.
The Return of Planescape? - Curious. There is a brief note on this 'countdown' at Enworld.
13 hours ago