I hated Gen 5 more than any others. I found the story, while more interesting than some others, to be painfully linear, particularly in black and white. The linear storytelling took a lot away from the games for me, much like in final fantasy xiii. It was the most excruciating formula I've experienced in a pokemon game where practically every city was the same pattern with meeting the gym leader, fending off team plasma, and then beating the gym. I also wasn't a fan of the experience adjustment as it involved a lot more grinding, especially because there were people blocking off the next area where stronger pokemon awaited because they were "dancing for no particular reason"
Also, while there are some pokemon introduced in Unova that I love, there are so many that seemed like cheap imitations of gen 1 pokemon, and that goes far beyond the stereotypical starter types, fodder bird and rodent, and early bugs. I wanted to see more individuality and creativity in creating new pokemon, rather than altered replications of existing pokemon that quickly became forgotten. And for the record, I have no problem with the ice cream cones.
And then there was the anime...
All that being said, Gen 5 did introduce several gameplay mechanics that are greatly appreciated, such as reusable TMs and some intriguing pokemon abilities like zoroark's illusion and darmanitan's zen mode. All in all, however, gen 5 is easily my least liked generation in the entire series.