I love this show to bits. As someone who grew up with Ash, Horizons is an exciting and refreshing take on the anime that I, for one, am all here for. Ash had most of his development in earlier seasons, meaning around when the Sun and Moon anime released, Ash hardly grew as a character, and his progress on teams in earlier seasons had reset.
Horizons, on the other hand is a true reboot of the Anime. The main protagonist characters, Liko, Roy and Dot, are much easier to relate to and get attached to in a shorter time than any of Ash's companions, and all get development to become better trainers and friends. The Rising Volt Tacklers are a great cast of secondary characters, especially characters like Friede and Mollie.
The antagonists of the show, being The Explorers, are a great new spin on the typical evil team that chases the protagonists around, with Spinel by far being the star of the show. He's hardly a pushover, unlike how Team Rocket sometimes came across, and isn't one to shy away from underhanded tactics to ensure his success. Amethio is also a great character, and those who liked Hunter in The Owl House (or characters on a similar vein) will likely enjoy his moments too.
Overall, Horizons is a great series. The lack of Ash should absolutely not be a turnoff for those wanting to try this series, as even without his highly marketable face, the show is amazing, and soars higher than quite a few of his own seasons of the Pokémon Anime.