Stressing out about forms, making sure every single number is correct, finding out that you somehow owe money, and the ever constant fear of an audit, both legitimate and random. Like getting teeth pulled without anesthetic. Why is it such a pain? Primarily the big tax prep companies lobby the system to stay this way. Oh well, that won't change. Too much money in tax prep for them to drop that cash cow.
@BlueVeins H&R is the worst. Will charge a small fortune sometimes. The real sad part is that taxes should be way more simple. All this stuff is reported, filing taxes is just a way to compare it to what the IRS already knows. In broad terms, the current system made the middle man essential.