The point of system neutral is so you can tailor it to your system of choice.
Personally I'm happy they're putting out a system neutral book. I have a bunch of the other setting books they released for various editions, and in 3e, and the other 4e setting books I've read, there's far too much crunch for the pagecount.
Its a setting book, not an options book. I want it to be almost entirely setting. That's why I didn't end up picking up Neverwinter.
The pagecount is atrociously short though, it should have been about 100 pages longer, and like 5$ more expensive. That, or it should have been like 8$ cheaper.
As someone who owns this, DotU, the 1990's Menzo boxed set, and 3e Underdark, I think its quite useful. It's a book I've been waiting for for a while.
1. It brings much of the info needed to do a quality drow game to one place.
2. It includes GM advice for running that sort of game.
3. It includes Player advice for playing that sort of game.
4. It gives history of Menzoberranzan outside the 2e timescale. (though annoyingly, virtually no info from 1372-1385DR - which is the time period I was most interested in)
If it had been filled with 4e crunch, I would not have bought it. It gets them sales outside the 4e crowd. Some people didn't find 4e to be the game they wanted to play.
Its a setting book. I wish my 3e setting books were this useful with 4e, or 5e. It's also not a player book, it's a GM book. Put the character options on DDI, in Dragon Magazine Articles. Its all you really need. Players will get access to the options through DDI, and the GM can buy the hardcover book.
I wish all settings were written like this, or "Return to the Road of Kings", or Kingdoms of Kalamar Campaign Guide.
They shouldn't only do this when switching editions though. They should do ALL the setting books this way. I'd buy more setting books. Maybe even just to read.
And I find the fact that it's written in "Align-Left" instead of "Left Justify" to be very odd for an RPG book, but that may be something WotC has been doing for a while that I just missed.