A little forewarning, I'm not running a 1E game.
I got this product for the 5E game I'm running. (The January 2013 ruleset is what we're using right now.) I wanted some Underdark stuff and these books work great. The story isn't terribly deep at first. For the Giants books, it's basically, "You're an adventurer, some town wants you to kill/drive off all the giants that keep attacking." Then you get the, "our princess is in another castle," at the end of three successive giant fortresses. The drow stuff is pretty cool though. The map of the Underdark is pretty good and there's a lot of stuff to fill time in for your PCs to make a more real world. However, the encounters on the map span three books. They don't really line that stuff up very well.
I'm also not planning on having my party fight Lolth. The Underdark is just a place for them to stomp around and for that, the books are phenomenal.