The biggest surprise for most people will be that they won't get a refund next year. While the intent of the reform was to reduce taxes for most people, the decision to change the federal withholding tables in 2017 is going to kill your refund.
Most people will owe less taxes, but they will also have less withheld from their paychecks. This means you get more money now, but don't expect to get more money in your paycheck today AND get a big refund at the end of the year. I think this is going to catch a lot of people off guard!