Pokémon

For me, it will always be first and second gen. I remember playing Pokemon blue on a very bare bones emulator before it released in my country or at least before I became aware of it. Later went on to get red, yellow (the one with Pikachu following you around) and silver.

The gens after that kind of added so much stuff that I wasn't interested in at all and that seemed to clutter up the experience. But maybe I just grew out of the franchise as well.