Umbran, brings up a good point. However I think an important distinction is being lost by a few folks here.
As Umbran stated:
Then, we had games which had rules (and stats) for almost everything under the sun, and we complained how bloody long it took to stat up the NPCs and monsters so fully.
So, now they give us a bit of a mix - all the combat stuff is statted out for NPCs, but the non-combat stuff is left to the DMs imagination. And still we complain.
If you're a GM that hates prepping monsters & NPCs, then
for your home-made adventures, minimal stat blocks are a very good thing.
However, if you're buying a
pre-made adventure - regardless of how long the stat block is, the GM isn't the one writing it up. It's been done for you already. No time wasted.
As for the 4e module approach, I'd say it leans closer to the opposite end of the "detailed bad guy/monster" than a mix. (YMMV.) The absence of motive, characterization, etc.
forces the GM to come up with it such things. That is unless the game is truly being played as a beer-n-pretzels skirmish game.
There's no right or wrong, here, just differences in taste/style.
If I take a step back from my own preferences for a moment and look at it objectively, though, I have two questions with regards to pre-made adventures:
1. Does the presence of additional, non-mechanical detail in an adventure increase or decrease the utility of the adventure?
2. When I buy a module am I looking for a traditional adventure (synopsis, plot, characters, statistics, maps, & locales) or am I looking for pre-built encounters & maps?
As a consumer, if I'm evaluating a module based on 1 & 2 above, am I getting the bang for my buck with the "lighter" module or the "fuller" module?
I suspect that there are a far greater number of GMs that would hold up
Crypt of the Everflame or
Sunless Citadel against
Keep on the Shadowfell as an example of good design. I also suspect that those same GMs would say the additional info provided better helps them to run the module.