Wii U

Nintendo advertising this as a Wii accessory, when it was actually a new console, really hurt this thing. Even people who played games didn't know it was a console. It looked like a 400$ accessory.

Second, I just don't see the point in having a second screen for 99% of games - unless you're doing an Elite Beat Agents type thing that needs touch, most of the time you're just pointlessly diverting attention from the TV - the user can only look at one at a time.