If we talk about actual fun, my answer would be Saints Row: The Third (actually all the SR games, but 3 had the right dose of goofiness).
If we talk about games we played or hooked us the most, then I'll go with Civilization V.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.