Hoenn is a fairly diverse region. There's a forest, volcano, falling ash in a route near said volcano, mountain, desert, and of course, water routes. (So many water routes, like half the region is water. In fact, Hoenn looks like a land/water yin yang, but then it fits the land vs sea theme, but I digress.) Even with the numerous water routes, it's the underwater that makes the water routes in Hoenn less monotonous and more beautiful. There aren't really any other regions with such a varied ecosystem, unless Kalos can outperform Hoenn in that regard. Even the man made buildings such as the Mossdeep Space Center, New Mauville, and the Weather Institute are wonderful. That, and the Pokémon in Hoenn are among my favorites (starters, Ralts family, Zigzagoon, Flygon, Roselia, Wingull, Castform, Metagross, the list goes on and on). With such a beautiful ecosystem, and the diversity of Pokémon, it's no wonder why Hoenn is my favorite region.