I'm afraid I disagree here: Best Wishes has made the Pokemon anime absolutely unwatchable for me.
As a character, I can't say I was overly keen on May. Partly because her character development was always put to one side for Ash's, and she was treated as little more than an afterthought. But Dawn, whilst she was extremely annoying to start with, was a fantastic addition to the cast, because she wasn't just a sideline character; her development was equally as important as Ash's, and the two worked well together (I mean that in a non-shipping way) to make the anime interesting again. Whilst I don't think Dawn should have beaten May in the Wallace Cup, I can understand why the writers did it, and her character did improve from that moment onwards. Coming in second place overall was, for her at least, quite the achievement, and she came a long way over the series.
Looking at things in hindsight, Dawn is perhaps the best member of Ash's party, because she actually went beyond the sidekick role to have her own character that didn't revolve entirely around watching Ash battle. Yes, Brock and Misty both have their own goals, but how often did we see those goals come over Ash's? Very rarely.
As for fillers...about 90% of this anime is filler. They travel, they find some random character who has a Pokemon they've never seen before, Team Rocket appear, they save the day, they move on. Rinse and repeat until the next Gym Leader or contest or whatever. They're all pretty much the same to me.
The Team plots are never handled well; its the same as in the games. They don't get anywhere near enough exposure to be little more than fillers themselves. If they're going to be the primary antagonists as such, they need to show up more than once every fifty episodes or so, and it needs to be more than just a token appearance as well, and they need to visibly accomplish something. Perhaps the only antagonist in the Pokemon anime I have ever been able to take even remotely seriously is Hunter J.
Best Wishes has undone everything that Diamond and Pearl built up: Ash is back to being a stubborn, idiotic little brat, and he has two new sidekicks with absolutely no character whatsoever. For me at least, there is absolutely no reason to watch the anime anymore, and it is going to take a hell of a lot for it to get out of this slump. This is just how I feel about it, though.