I was recently flipping through the 4E PHB and the DMG and I think I have to apologize for the direct or implied criticism I made back here and here that 4E is not a rules-light game.
In looking a little closer at the rulebooks I would say that it is in fact a rules-light game. The core rules a DM needs to know to run it appear to only be about 70-80 pages in the PHB and another 100-ish pages in the DMG. The pages and pages of character racial and class powers - which make up the bulk of PHB and PHB2 - and the monster statblocks in 4E are not really rules the DM needs to know to run the game. They can just be referenced as needed. That is just a little bigger than my beloved B/X (of course the 128 pages of B/X do include monster statblooks).
So my apologies 4E. I am still not too sure what I think of you otherwise but I do now consider you rules-light.