When you're disenchanted, you're disappointed or let down by something or someone you once admired. Large classes and standardized testing often leads to disenchanted teachers.
An unsatisfying final episode of a popular TV show's last season will result in disenchanted viewers, and the impression that all the candidates are basically the same means a lot of disenchanted voters. When you're enchanted by something, you're delighted by it. This comes from the Old French root enchanter, "to bewitch, charm, or cast a spell." Adding the prefix dis- gives disenchanted the opposite meaning.