Rule-lite or Rule-heavy describe THE perfect ideal ruleset

[solomoncane]

I really liked the scalable complexity that Heap described earlier.
This is essentially what I do with different rule sets (True20, 3x, & GT/Modern).
You need a streamlined version, a non-mini tactical version, and a full-battlemat mini extravaganza version, each building on the other.
A blending of the rulesets with a point-buy option (smash M&M, BESM, and Point Buy Numbers together) would be the ultimate thingy.
All core rules should be in one book and be sufficient to begin campaign building. The things that take up a lot of space (spells, monsters, and magic items) should all be template-driven to allow on-the-spot creation without extensive lists of stat-blocks.
If WOTC wants to publish this, they could call it something like "Dungeons & Dragons presents Ultimate d20", thereby taking advantage of the brand identity w/o tainting the ruleset w/D&D-only rules.
Once this core book is created, genre-speciifc supplements could follow such as Ultimate d20 Dungeons & Dragons Fantasy, Ultimate d20 Modern Spy, Ultimate d20 Space Opera, etc.
Whether or not the core is OGC is another debate.

 

[der_kluge]

Honestly, this (and everything else in your post) is exactly what Grim Tales provides.

Oddly enough, I own Grim Tales, but haven't really read it. I've tried, but you know.. time is hard to come by with a 2 year old. I'm still committed to reading it, though.