What Champions Online has going for it:
Lots of powers
You can mix and match those powers and upgrade them with abilities that alter how they work.
Their super-running can go up walls.
What City of Heroes has going for it:
Good story for each of the villain groups, with the story weaving between the groups.
Heroes that can take on multiple mobs that are their level (i.e. they FEEL heroic).
Great power pools that aren't duplicated anywhere else (teleport foe, AoE holds, etc.)
Playing in a group increases complexity and fun for the game.
What Champions Online has going against it:
Cell-shading
Stories the characters don't get invested in
Due to the ability to select any power, the powers must either all be equal, or there will be poor choices and amazing choices.
What City of Heroes has going against it:
When selecting different ears, you should have the choice to remove the normal ears (cat ears, bunny ears, etc.)
Not all the powers in a power pool will be appropriate for a character's theme.
Caves.