The Netflix App on my Wii.
...
I find it difficult to pick any game in particular. The games I played the most are not games that I felt defined the generation for me. Animal Crossing City Folk, Monster Hunter Tri and Modern Warfare/Black Ops were all very high on my 'most played' list. I enjoyed those games immensely despite their flaws. This is most likely due to being multiplayer. The social aspect made them that much more enjoyable. No single game sticks in my mind so much as the unique gameplay experiences. Motion controls, pointer controls, touch controls, playing plastic instruments, these are what defined the generation for me.
So really, my idea of playing a game has broadened to include a plethora of experiences both solitary and communal. Everyone has different tastes, but the one game on this list I think everyone should experience is World of Goo. Boom Blox can get a runner's up acknowledgement.
Single Player Experience
1) World of Goo - Wii/PC
2) The World Ends With You - DS
3) Minecraft - PC
4) Civilization 4 - PC
5) Plants Vs Zombies - DS/PC
Multi Player Experience
1) Modern Warfare - Wii
2) Monster Hunter Tri - Wii
3) Boom Blox - Wii
4) Animal Crossing: City Folk - Wii
5) Rock Band 2 - Wii