One of these screenshots above is from New Super Mario Bros. U. The other is for New Super Mario Bros. Wii. Move the slider back and forth to compare. Can you tell which is which?
Try this set, too.
How about this one?
The Wii U image is the first shot in all the comparisons. What you can't appreciate at this size and resolution is that the Wii U images are made to appear in high definition; the Wii's don't. And the games are different in other ways. The Wii U game has special score-attack modes and lots of special Yoshis. It also has an elaborate overworld map reminiscent of Super Mario World.
Shall we compare them in action?