Gaia is the idea that the planet is adapts to make life possible in some way I didn't understand. Anyway my natural gut feeling would be to slag it off as hippy shit, but my impression from the book is that there is a lot of published work in Science/Nature. In fact Lovelock sounds like one those scientists who reminds people of their achievements at every opportunity.
Although he is a hero of the environmental movement, he was very keen on nuclear power, and less happy with wind farms.