Doc Love is useful ONLY as beginner material for the recovering AFC who may be just getting started. Doc concentrates more on hard-and-fast rules such as "wait seven days to call, be a challenge, have confidence" etc, without getting into the deeper reasons why these rules are so. He just attaches these concepts to his "Reality Factor" which if denied will cause "pain." Fair enough, but to really improve yourself, a reader need to know WHY these rules are true.
However, having some hard-and-fast rules can be temporarily helpful for newbies who would for example call a girl too quickly out of desperation. Of course, there are instances where you can call in less than a week with the right mental frame, but Doc doesn't take this into account.
Additionally, Doc's stuff is getting dated, and in my opinion his "Sal The Fish" schtick and his infamous photo with the poodle and vanity plate only serve to damage his credibility. Not to mention, his Dating Dictionary has no flow whatsoever and is essentially an alphabetical rambling of his theories.
At this point the System is just a cash cow for him and he has no fresh contributions to add to the community, as evidenced by his three "Mastery Series" which are primarily just reprints of his existing and freely available Q&A articles.
Doc was my first step into the seduction world when I had my "ah ha" moment almost five years ago and realized that the one thing in common with all of my dating failures was me. Doc's stuff gave me my first steps out. There are some good ideas and rules in there, and despite my criticisms I do recommend the System, but as I mentioned, only for the absolute beginner. Read it, get the useful stuff out, but after slugging it through the Dictionary, DO NOT stop your reading there, or you are not reaching your potential.
In my opinion, it's primary strength and it's immediate benefit is learning how to flush out insincere women who will take advantage of you. I believe for someone getting started this is the most important defensive skill to learn. Once that shield is up around the heart (and wallet) the real work can begin.
David D has obviously much better and deeper stuff, and the evolutionary psychology books he sources such as Mating Mind, Red Queen, Selfish Gene, Sperm Wars, etc, really get to the absolute core of why the game works as it does. My view of the social and dating world has permanently changed as a result of those reads, and I have far more perception and control over my own destiny. Doc can or will not provide this level of understanding.