We just got a Wii recently and I have to say my favorite game is the bowling on the Wii sports. We have also downloaded several games from back in the day for the original nintendo that I enjoy playing.
worst game.. Red Steel? It was very difficult to control. A little bit frustrating to be struggling with the controls while yakuzas are running at you.
Guitar Hero III. A little tough for the real little kids, but great for the 8+ crowd (including adults). Plus if you connect it to the internet you get to beat 7 year olds (or other parents making believe that they're 7) in guitar battles. LOL
For the younger crowd, my now 5 year old Charzilla loves and is great at bowling and Cooking Mama.