DP did have some bad fillers but all the plot-driven episodes made up for it.
Now that i think about it,most episodes in Sinnoh were indeed plot driven being focused on storyline. Like i said before, DP was probably region which had most detailed character development treating plots and story rather well. Dawn contest arc was massively fleshed out, Ash made biggest progress as trainer and lot of attention was given to game characters.
I believe DP was best when it comes to rivals with Paul being most fleshed out and developed rival Ash so far had,and whether you will like or dislike Dawn rivals you cant deny that Zoey, Kenny and to lesser extent Ursula influenced Dawn character bringing tension, serving as push which is supposed to advance character forward in attempt of catching up with them.
However if there is one thing i disliked about Sinnoh, was that too many episodes were focused on pokemon training and perfection of attacks. Many DP episodes despite being focused on story lacked humor and entertainment being rather bland and i have to say how BW is so far better in that aspect. Most of its episodes have good dynamic between characters and are actually funny. If DP had less episodes which focused on perfection of attacks i would be more satisfied with this saga and it wouldnt have hurt if we got some surprising cameos from older characters like Misty either.
Nothing compared to AG and onwards OS as a whole was like a test in my book. Most for some reason think of Johto as separate from OS. no idea why. I liked Johto over the first half of OS. Kanto is kinda boring tbh.
Im asking myself same question too. Whether people like it or not, Johto was part of original series with first 5 seasons having title "Pocket Monsters".
Johto had its flaws,but it had more to like than dislike imo. Misty and Brock got more screen time and battled more than they did in Kanto, original trio still had great chemistry having several memorable moments there, we had some great arcs like Whirl islands and its cup, Red Gyarados, Larvitar, mini story arc with Clair, dragon temple and Dragonite and Silver conference was one of best leagues pokemon had imo. As for fillers most of them were actually funny bringing entertainment Like "Heartbreak of Brock", "Hook,line and Stinker", "Hocus Pokemon" , "Snubull Snobery", "Fortune Hunters",One trick Phoney etc.