I do not like Advanced Generation.
First, I was annoyed by the way in which it characterized the TRio. Eighty five percent of the time, Jessie was depicted as being entirely cold hearted, selfish, and dumb while James was shown as being Jessie's (and to a lesser extent Meowth's) angsty victim. Meowth took an even worse toll than the duo. Most of the time, all he did was have erotic fantasies about Giovanni. Though I like Meowth's Giovanni fantasies, he should have been scheming just as often as he was fantasizing about Giovanni.
I may dislike DP, but I am glad that its Japanese version has mostly steered clear from the way AG portrayed Jessie and James (they are still a mess in the dub). DP may have a couple of episodes that depict Jessie and James poorly (especially early DP), but there are not nearly as many as there were in AG. Unfortunately, Meowth is still characterized similarly to the way he was in AG.
Second, I disliked Contests. They are the equivalent of boring pet-shows that one can watch on TV. I am hoping that they will not be in Generation V, since they not only dragged down the quality of AG, but have also done the same to DP.
Third, I thought the storyline with Teams Aqua and Magma was rushed and poorly developed. Considering they are the major criminal organizations of Generation III, the plot surrounding them should have been better handled. I was happier with the way in which the anime handled the Team Galactic storyline. Even the Team Rocket storyline, which has yet to finish, is better than the Aqua and Magma story.
Fourth, I thought Ash and May's rivals (baring Harley in May's case) were bad characters. Morrison was obnoxious while Tyson was a bland Gary-Stu. Drew was an irritating Gary clone who just wanted to get into May's shorts. While we are on the subject, Contestshipping was aggravating. It was a cliched love-hate relationship in which the guy loves the girl but he mercilessly teases her and the girl loves the guy despite the fact that he is a jerk to her. Why people are so impressed with it is beyond me (then again, I cannot fathom why people like Pokeshipping, either. Still, unlike Ash and Misty, at least May and Drew were not abusive towards each other).
Fifth, I did not like how Ash went from being a hot-headed and arrogant idiot to a boring hero-boy. At least I could enjoy hating him in the original series. However, he was so stale in AG that I could not even feel that way towards him. The same applies for his character in DP, though I find him more tolerable there because of his relationship with Angie.
Sixth, I thought the vast majority of its filler episodes were awful. Many claim that all of Johto's fillers were bad, but Johto had just as many bad fillers as it did good ones. Only a few of AG's fillers were entertaining. Ninety five percent of them were insipid.