Well, when the show started, they were kinda funny, but they could also be serious when needed. By around Johto, they started becoming stale. Through Hoenn and Sinnoh, they felt like they were just THERE. Even more so in the movies where you could often times remove them from the plot and nothing would change. In Unova, they started becoming DEADLY serious. After 14 years of doing the same thing (spout motto, kidnap Pikachu and/or mon of the week, making annoying and unfunny lines and rhymes as they go along), it was a nice change of pace. And now it looks like they're going back to their "funny" roots, which negates their more competent tone and irks people.
That's why all the hate.
(and if you say "well kids find it funny", I seriously think you underestimate the intellegence of kids)