What's with 'Her'?

We went to see the movie 'Her' this afternoon and I must admit that I am completely puzzled by it's inclusion on the list of nine movies nominated for a best picture and four other Oscars.  It makes 'Nebraska' and 'Inside Llewyn Davis' look like masterpieces (which they're not).  Joaquin Phoenix gives a very low key (nearly somnolent) performance as a recently divorced ghostwriter of other peoples' personal correspondence who falls in love with an operating system (voiced by Scarlett Johansson).  Every time he went to bed (very often) I wanted to close my eyes and go to sleep. The entire film flat-lined in the first 15 minutes and then went on for another 2 hours.