In my opinion none of newer sagas managed to capture same level of emotion, humor and creativity like Original saga did.
Now i liked Hoenn, DP and BW improving in some aspects, like battles becoming better, writers developing characters and story better,rivals being properly treated etc.
But in OS in my opinion pokemon used to have more emotion and personal touch put into it with writers straying away from game canon to significant degree with anime being more focused on prospect of adventure, there was more humor, more references to Japan culture and you could get feeling that pokemon wasnt so much subbed to game promotion having bigger individuality. Anime felt fresh and new at that time with writers experimenting with several things to determine which works or doesnt adding that extra flavor to show. This can be noticed in real guns being used in first season, Ash having crush on girls(like Giselle)etc. I liked wacky plots and humor Kanto and Johto(to lesser extent) used to have like St. Anne, Island of Giant pokemon,episode about giant Tentacruel, Gengar or Alakazam trying to destroy whole towns etc with writers sticking less to games adding more of their own personal touch.
Misty and Brock also played important role in here being like Ash coaches and mentors helping him to grow as trainer over course of OS while giving us insight in their own lives and past pursuing their own dreams.
Each episode felt fresh bringing something interesting within itself and rich mount of references to Japanese culture and less censoring was bonus too(although this led to certain episodes ending up banned).
And chemistry between original trio was arguably best out of all groups we had so far in pokemon as far as im concerned having very close bond and strong friendship . Group played out very well having good dynamic and charming interaction. From Ashs naivete and stupidity, to Misty sarcastic remarks and funny moments of anger and caring side acting as push for Ash to be better when doubting in him to Brock figure of being like older brother to them providing his knowledge and tips in needed situations.They felt like close group of friends which fulfilled each other in genuine, natural and enjoyable manner making things worth watching.
AG comes in second place though, with quartet of Ash,May,Max and Brock functioning well liking different kind of dynamic which was present between this characters with Ash becoming more mature becoming ready enough to take on mentor role to May with things changing up,and inclusion of Max served nicely too sharing many things in common with Brock which allowed for good character interaction.I also liked May contest arc having some great rivals(like Drew and Harly)and Jessie deciding to become coordinator was nice and unexpected change of pace.
As for DP series,they currently share third place with Unova.
It had good characters individually with Dawn being good character, liking her attitude, story arc which resulted with great finish almost winning whole Grand Festival on first attempt and rivals were fine. Ash got some great progress through whole arc, with writers finally giving him proper rivals with Paul playing out well his role with their rivalry having great development and finish at Sinnoh league which was surprising and good with return of Ash older pokemon being a plus.
However chemistry between group was least coherent not having good bonding ,Brock barely got any screen time, too close following of games and neglect of some previous characters from past takes up some points from it.
Also its little to say how repartition of screen time was incredibly unbalanced giving too much exposure to certain pokemon and humans like Ash and Dawn, while leaving shafted everyone else.
Along with whole gym and contest quest feeling dragged out lacking adventurous and unexpected twists at times some other series contained in my opinion.
When it comes to Best Wishes series feel like step down in some aspects,though there are few things which sparked my interest for this saga .Such as:
Chemistry between Ash,Cilan and Iris having lot of enthusiasm and energy with clashes between Iris and Ash,dissidence between Iris and Cilan about science and mutual respect and admiration prevailing between Cilan and Ash allowing for some great interacting. They have second best dynamic in pokemon for me.
Team Rocket becoming more competent and actually threatening is definitely one of best refreshing changes we had in years with Jessie and Jams new role being given by Giovanni making them actually competent for a change instead of being treated like punching bags all the time. Though as most ideas in BW this was executed poorly and in forced manner happening without proper explantion.
Don George tournaments seemed like nice change of pace liking format they followed and way how to gather all character riuvals at one place brimming with lot of fluid interaction and great dynamics too.
But inadequate and poorly handled development of characters, Ash drop of skill and experience, league and resolution of rivalries being rushed and executed badly along with play of events happening in inconsistent, contrived way prevent it from being truly endearing and enjoyable saga for me. Still appreciated some of creative premises they originally wanted to go with.
The reason people thought DP was boring was mainly because of Brock. Yes, one character ruined the series. Why? Because he screwed up the group dynamics.
People mainly enjoy the anime for the chemistry of the main characters. Because the writers made the mistake of keeping Brock for DP, it completely destroyed any potential chemistry of that group. Ash and Dawn had decent interactions, but Brock had no chemistry with Dawn whatsoever, and since Dawn was treated as a co-star, it made it even more obvious that we had two leads and Brock was a one-dimensional background character.
Brock ruined Dawn's character too. As people noticed, Dawn started off as a fun character in early DP. After the trio was settled, Dawn got a bit blander because she didn't have interesting characters to bounce off of. Brock was useless, so Dawn didn't work well with him. Dawn would have been a much better character interaction with any other male as seen with Gary, Paul or Barry.
So basically Brock ruined DP for some, whether people realized it or not. That's why the writers finally got rid of him, because Brock overstayed his welcome by an extra generation.
I never got such impression personally. Brock was fairly enjoyable as far as his personality goes still chasing after girls, being knowledgeable and intelligent group member teaching Ash and co to prepare medicines, had memorable moments with Croagunk, Happiny or Nuzleef allowing that his expertize come to expression along with playing nice role in tag tournament, when scolding Paul for way he ftreated Chimchar, Marilyn which valued pokremon strength by looks etc. In Team Galactic arc and lake trio he had valuable role too.
If there was problem with chemistry between DP cast that wasn't Brock fault but in reality lack of focus on group dynamics as whole. Writers in general focused tone of series more on battling, pokemon themselves and their development rather than on humans and fleshing out each other through interactions and vivid dynamics. That was probably reason why it felt lifeless at times and too much emphasis being put on development of Ash and Dawn and their progress as "two stars which progress through show", often leaving Brock out of group interaction. Hardly his fault.
Something which was mistake with writers making sure to fix that in BW with no one in BW cast feeling left out.
Regarding his departure, i don't think that was reason behind his leaving and it would be abit presumptuous to generalize things so much conjecturing how "everyone were bored of Brock". Im pretty sure main reason Brock got replaced was because of BW games revamp trying to give "vibe of fresh start"with several changings happening from contests being gone, older pokemon not appearing, TR becoming competent, Unova being portrayed as far and isolated region, Ash getting regressed all with attempt as well not having anymore second side quest.
Writers probably wanted to mirror those changes with anime going back to formula of one main star and two sidekicks as well why another new character joined main cast at expense of Brock leaving. To better promote "new beginning" cutting ties with past.