I took a cursory look at Colorado since it's my home state. Overall participation was very slightly higher (+11,000 votes 2016 vs. 2012) though with population growth it's probably proportionally lower. Pretty close though. In terms of net votes vs. 2012, using Obama and Romney's totals:
Clinton -115,006 votes (-8.7%)
Trump -48,889 (-4.1%)
Johnson +93,538 (+263%)
Stein +25,501 (+340%)
McMullin + 26,715 (not on 2012 ballot)
So instant analysis for CO, which Clinton won by a smaller margin than Obama did, looks like third party candidates made the biggest difference.
Will be taking a look at all 50 states and in particular states that passed voter restriction laws (in CO it's really easy to vote).