I have to admit I never liked that expression, among other reasons for its sheer reductionism. Having read some of the things Lewontin wrote, it is hard to accept such deterministic, panadaptationist, gene-centered narrative.
So you can imagine how happy I was when I came accross this article: Die, selfish gene, die.
It is very well written and a clear presentation of recent advances in genetics and evolution that make clear the sheer inadequacy of the "selfish gene" model.
And I’m not alone in this appreciation; PZ Myers wrote approvingly about it: Higher order thinking.
And given the backlash, he returned to the subject, with gusto: The reification of the gene.
I thoroughly recommend reading all the articles. They should be worth credits in any Biology course.
In a nutshell, it’s the complexity, stupid!