NTSC signals display in 720x480, while PAL signals use 720x576i -- hence the horizontal bars, which are somewhat understandable. However, displaying 50Hz signals on 60Hz sets cause a noticeable slowdown that, according to Orry, "has plagued [PAL] gamers for years. Now PAL gamers are used to proper PAL conversions and 60Hz gameplay options, and being forced to return to the 50Hz dark ages isn't something Wii owners expected."
Not all games suffer the same fate. In an e-mail to Joystiq, Orry notes that he has not tried other titles yet. CVG found similar problems with F-Zero, while Mario 64 and Donkey Kong Country (SNES) ran smoothly with no problems. For now, it's a grab bag.
We know Nintendo promised "faithful recreations" of its old games, and we know that some European gamers won't mind the slower-than-NTSC pace, but to others it's considered lazy on Nintendo's part to bring a game with obvious technical maladies. The Wii comes out in Europe this Friday, December 8.