While Sun/Moon are good games, the Ultra games were easily the most pointless of Pokemon's definitive editions. In some instances it made it worse, like with the Lillie story near its end. Or Ultra Necrozma, which design-wise is pretty cool and a notoriously difficult fight by Pokemon standards, the area it's encountered in was incredibly disappointing. It was definitely this game where Pokemon's decline in quality started to affect my perception of the series at that point.