...okay, I have to admit I don't have anything for Q. Instead, I'll just launch into some freewheeling thoughts regarding classic D&D that have been rushing through my mind of late.
AD&D2 is a good system. There are a few things I don't like about it, and a few subsystems that are a bit too complex for my tastes, but on the whole it's flexible enough that the rules tend to get out of the way when they're not needed. Plus, I know it better now than almost any other system, and it's what I moved my current group to, so I'm sticking with it.
B/X is also a good system. It's very tightly designed, simple in a lot of places but spelled out where it counts. The only thing I don't like about it is race-as-class. Yes, I realize that the focus on archetypes can be interesting, but when trying to design a believable world, it ends up looking a little silly. For a pure "game", this would be my go-to rules set.
OD&D has been almost beckoning to me of late. Ever since I printed out Greyharp's Single Volume Edition and had it spiral-bound, I've realized that its nature as a framework is actually perfect for my own campaign. There are a few rules I can easily change, but I actually like the idea of designing a world to fit the rules. Plus, the blood-simple mechanics and lack of later developments (such as item/class/spell bloat) make it a perfect edition to run a human-centric campaign set a century or two before my AD&D2 campaign. (This also gives me an excuse to have hobbits by their real names!)
Those are my thoughts for now.