Pokemon Emerald.
Emerald was my first Pokemon game, and I haven't stopped loving not just Emerald but Hoenn in general. It was much more origanal than Johto was at being a new region and it really set the bar for the latter games, with like trio masters, a variation of differences between the prequels and itself, and more. What I like most is the unnatural occurance that happens only the generation's sequel, like in this case it is the clash between Groundon and Kyogre in which Rayquaza fly out of the Sootoplis skies like a badass and tells them STFU BOTH. It's a boss game in general.