I don't have any first-hand knowledge of krav maga, so all I can really go off of is what I've read and seen online, and from a couple of people who have tried it.
Their demonstrations all seem to be of the sort of pre-set memorized techniques that plague most of the traditional martial arts, like aikido, some karate, and the like.
I see stuff like this:
and I become very skeptical and see little value in it.
On the other hand, I have spoken to a couple people, and heard stories that krav maga training can be seriously hardcore, in terms of conditioning, discipline, and training scenarios, and the like.
So, as someone who hasn't tried it, my feeling is that krav maga is an art that would make you a tough motherfucker, but isn't necessarily one of the most effective martial arts out there.