Comey never should have discussed a criminal investigation against Hillary 2 weeks prior to election, but Comey concluded that Hillary's actions were not criminal.
Mueller concluded that Trump obstructed justice, but decided that he a sitting President cannot be charged under DOJ policy, but Mueller made clear that Congress has the constitutional authority to act. Unlike Comey not finding that Hillary committed a crime, Mueller (Vol II) clearly found that Trump obstructed justice, and acted with criminal intent.