As far as animation with SM goes, the main issue people have is Ash's face which looks so jarringly different and overall a bit awkward compared to every other appearance.
Other than that, a major issue is the plot with having to go to school. The reason they have for Alola's rules and Ash being forever 10 is justifiable under normal circumstances, but Ash has a good 52 badges, 7 Frontier Symbols, is Orange League Champion, and can become a Hoenn Frontier Brain whenever he so desires. He should fully be capable of testing out of school or overall being exempt as he should know more than what the school will teach from his previous travels and be allowed to journey normally. It also creates a point with too many companions with Sophacles, Lilie, Kiawe, Lana, Mallow, and to an extent, the RotomDex and Kukui all being companions for his misadventures in addition to the occasional "character of the week" type which has more people than normal to keep track of and can deter some focus from the actual star. This is roughly double the previous record of characters in "Team Twerp" which was only 4 in Hoenn & Kalos.
Who knows? Maybe since Ash actually goes to school, he won't be stupid anymore.