My thoughts are opposite of those who loved Hoenn but hated Sinnoh.
I thought Hoenn had dopey starters, and to be honest I hate all three of them. They just look....weird. They didn't add anything new. And sure there are a handful of cool new Pokemon (hello Aggron yo?) to catch, but for the most apart, again I hate them. But I did like the map a lot, I don't know why others don't. I thought it was diverse and fun to trek through; it came out as a bright spot in the game.
For me, Sinnoh did everything right, that I thought Hoenn did wrong. The collect of Pokemon just kicks a** and I like the map even more.
Another thing is, Hoenn was just a pure step backwards from Johto. Day and night, arguably the coolest new feature was scrapped! The new teams, Aqua and Magma, were friggin lame and came across to me as a ham-handed environmental statement, don't get me wrong I'm not against political allegories but they don't fit Pokemon. They weren't even intimidating, the captain of Aqua looked like a retro porn star! The idea that Team Rocket were just thugs in it for the money, made it a lot more fun to bring them down.
Speaking of scrapping things, what happened to a genuine rival? May was a joke, you only got to battle her a handful of times and I think you battle Wally like...twice,he wasn't very tough either.
Just the whole game, feels like a watered down version of Gold and Silver which is a huge disappointment condsidering the vast technological advancements. And when Game Freak released Fire Red and Leaf Green it was kind of like, yeah just forget those games happened, here's a bada** remake
To each his own though I understand entirely why one would hate or love Hoenn.