Everything since then has been a combination of algorithm and compsci research (which they are world-class in; credit where credit's due), vague ideas about things people might like, and copies (or buyouts) of their competition. They remind me of my engineering friends who tried to come up with business plans in college...good at building things, but clueless about figuring out what people actually need, what they should therefore actually build, and how to make it user-friendly. You know, all the stuff that you need if you want to run a business. (As I've said before on hn, their initial competition against youtube is a great example of this)
It's a surprise that a technology came along which upended them so abruptly, but it's been clear for a long time that they were only alive because their search engine couldn't be beat, and they didn't have a clue how to replicate that success.