Someone else commented here in a past thread that the biggest cliff happened when Amit Singhal left Google and the AI lead John Giannandrea replaced him.

John Giannandrea brought about more AI heavy search and forced 'natural language' queries down the throat of everyone.

It obviously makes google money and is the right tool for popular queries. But for anyone doing more 'power user' searches it is just inept and I agree with GGP duckduckgo is now a better search engine for more complex queries.