The lance is unique among weapons with similar damage dice by having a 10-ft. reach and being one-handed when mounted. But the 10-ft. reach comes with disadvantage when your target is within 5 feet, which makes it a little worse than other weapons.
The trouble I see is that you're regularly going to be suffering that disadvantage. If you're a paladin on a charging horse, your first attack is a 10-ft. reach attack with one hand, but your opponent will instantly get closer to you after your first attack, making the second attack always from 5 feet and therefore with disadvantage.
I don't see this a very good.
Under what circumstances do the unique benefits of the lance outweigh its unique drawbacks? What tactics maximize those circumstances?