Johto was kind-of boring, even-though regardless I think I agree since I'm biased. Still original Pokemon > Johto Pokemon though.
Ash had an edge in the original series he never really got back. He became rather stand protagonist after.
Music was all around peak.
Nostalgia
Pokemon at their best.
Funniest/Most memorable moments
Epic moments
Great story-lines
Did not become indistinguishable from American cartoons. Kanto was an Anime & that's obvious.
Related to above, but Japanese references you don't really see anymore I think.