I think Idris Elba being left out is the central mistake the academy has made.
I recently read an article on the statistics of the film industry and the oscars - while White people are over-priveleged in their roles and the awards they get, Black roles and awards are pretty much proportionate to their industry presence and the size of the demographic in America. The real losers are the Asians and Hispanics.
But Idris Elba not getting a nomination has brought the issue to light, because he definitely deserved one.
Out of the nominees, I think the Revenant deserves to be there, and I havent' seen the Danish Girl, but I would put Elba's performance ahead of Damon's in the Martian, and probably Cranston and Fassbender in Trumbo and Jobs.