Maybe "good" isn't the right term, I have several other friends who watch anime dubs good and bad with no issue, but cannot stand the modern pokemon dub.

I tried to see the difference between how it was dubbed over the years and what makes the modern one unappealing. I don't have any actual conclusion but here's what I found.

Ash Ketchum's dialogue in the modern series is incredibly "literal" even when it's not an accurate translation of the japanese transcript. The weird thing is this isn't tied to the change between 4kids and TPC. Ash between Johto and Sinnoh is far more likely to use idioms and sarcasm that an English-speaking child would recognize.

Prior it was a lot of bad puns and after sarcasm is almost entirely gone. Ash and other characters say exactly what they mean with little to no wit whatsoever.

Alternatively, even if the previous dialogue was more engaging(to some), it was most certainly not faithful to to the japanese and would often improvise jokes in place of dialogue that is unrelatable to westerners