Don't worry about one-per-franchise, games are games.
Here are my top fifteen games of all time. This was a very difficult list to make, so if a favorite of yours didn't make the cut, then so be it.
#15: Crash Tag Team Racing (Crash Bandicoot, Xbox)
#14: Disney Infinity (Disney Infinity, Xbox 360)
#13: Super Mario Galaxy (Super Mario, Wii)
#12: Paper Mario (Super Mario, Wii Virtual Console)
#11: Left 4 Dead (Left 4 Dead, Xbox 360)
#10: Left 4 Dead 2 (Left 4 Dead, Xbox 360)
#9: SpongeBob SquarePants: Lights, Camera, Pants! (SpongeBob SquarePants, Xbox)
#8: Mario Sports Mix (Super Mario, Wii)
#7: SpongeBob SquarePants: Battle for Bikini Bottom (SpongeBob SquarePants, Xbox)
#6: Donkey Kong Country Returns 3D (Donkey Kong, 3DS)
#5: Tomodatchi Life (Tomodachi, 3DS)
#4: Mario Kart 64 (Mario Kart, Nintendo 64)
#3: Mario Kart 7 (Mario Kart, 3DS)
#2: Mario Kart 8 (Mario Kart, Wii U)
#1: Mario Kart Wii (Mario Kart, Wii)