A lot of the slapstick, especially in SM. Sure it's often silly and overdone, but I dunno, I enjoy it. I like clownish characters, and while it's emphasized to sometimes ridiculous levels, it never really feels like it's grinding the plot to a halt.
I like the Ash slapstick that is so divisive, and for some reason I love it when female characters get in on it, maybe because it's a rarity in many cartoons (and even the recent anime has started to dial it down). I love characters that can be competent but still make complete buffoons of themselves. Dignified heroes are overrated.
I love it when Ash is on a long winning streak and pretty much never loses a battle, like Ash's year long winning streak in Kalos. While some losses are needed for the sake of more development and make the anime more interesting, I feel that winning most of the time is nothing bad especially if you are struggling a lot to win and overcoming high stake situations in order to get the win.
As mentioned by Brock in one episodes, battles should be more about displaying skill and personality rather than just who wins or loses. I usually don't like characters who win all the time, but that's often more because they usually win generically and easily or have plot armour start to play more into their victories, they rarely keep the balance of them still looking fallible and injecting enough character into HOW they win. Let's face it, a hero has to regularly win stories, but there are so many franchises that don't even try to make it entertaining.
Ash's SM battle run hasn't been too bad despite emphasizing a winning streak since they still tend to emphasize his eccentricity (not to mention jobber battles like Team Rocket/Skull are kept to a minimum this series). His four main battlers have all taken token beatings (arguably far more than any of the other trainers' Pokemon this series) so still have a palpable degree of fallibility.
The only thing that kinda bugs me is how it always tends to fall in his favour when it comes to the Z Moves, with his opponents regularly failing or getting avoided, but his always working perfectly.
I do admit I'm one of those that tends to take too much gratification when one of the twerps actually takes a hit back in battle (I unhealthily savored Meowth actually Fury Swiping Pikachu at long last in the XY Pokeball factory episode, regardless if he still lost, he got in ONE hit, the perfect one sided streak was broken). I prefer even handed fights and when the hero struggles a bit, and of course in earlier series where the majority of climaxes were Team Rocket or legendary focused big arcs, that didn't happen a lot. When there's a bit of pressure on the hero that makes them put real effort into win, then I'm all for rooting for them.