I don't like them to be honest.
Many of them are weird (Lileep, Cradily, Zigzagoon, Breloom, Castform, Kecleon, Chimeco, Mawile, Sableye, Ralts, Nosepass, Gulpin, Spinda, Trapinch and Bagon just to name a few), not cute at all and some are ugly as hell.
Even the starters look like someone had like nine designs on a table and then he randomly picked three of them while having his eyes closed. They don't share any characteristics with eachother and look like they have nothing to do with each other.
Of course, there are some I like a lot (like Cacturne, Numel, Camerupt and Altaria) but 95% of them are... Nah...
I didn't like the region and I HATED the water routes (TEN?? TEN?? EIGHT OF THEM AT THE SAME TIME???) and music (Irritating. As hell. All of them). Also the storyline sucked badly. And the sprites... Awkward.
I hated the running sprites. The player characters, especially Brendan, looked like they were having a wank while running...
I was so glad when I found out that Sinnoh didn't have as weird and ugly Pokemon as Hoenn. And less water routes and an interesting region and better storyline. And better villainous team (Team Aqua/Magma= Let's make a world without water/land!!! Really??).
I don't like Hoenn, mostly because there was too many new things (double battles, natures, abilities, EV cap), bad region and pokemon in one game. All that introduced at the same time... It felt too much for one game.