>>54135373pullrates are the biggest objective factor.
other than that, it depends who you'e talking to.
actual players like sets that shakeup the meta. They are fond of new sets that give them and their decks new tools.
Investor types want a set with lots of expensive cards that is printed in low numbers. To them, Evolving Skies is a dream set because they can hoard it and make profit. Battle styles was bad to them because it was overprinted with few desirable rares
similarly, Gamblers like exciting rares. They enjoy opening packs looking for "hits" of dopamine
-Both of these groups kind of don't understand/care about pokemon and all the commons and uncommons are basically cardboard trash to them. Its all about the super rares
Normies, love consensus in general. They sniff out HYPE and CRINGE based on the reactions of others/ the majority. They like Umbreons and Charizards
Collectors like easy to collect sets. Celebrations was a great set to collect because it was small and relatively cheap to complete. Nothing worse than a fuckhuge gigantic set like fusion strike or an overpriced set with TERRIBLE pullrates like evolving skies.
Then there are just, pokemon fans/ art appreciators. They like a set with consistent theming or really good artwork. Battle styles isn't terrible to them, because it focused on a specific area/region, and was themed around martial arts and training. I wish more sets had clearer theming but I think I'm a minority and probably sorta autistic.
fusion strike was shit for everyone. Its theme and artwork and sheer volume of cards was fucked up because some dinky japanese battle set got rolled into it. This added so many weak trash cards as a result. Lots of ugly bloat and very few rares. Expensive. unfun to open.
early SWSH was kinda bad and so is early SV so far, but its hidden by the fact that they include a ton of easy to pull full arts now. a good strategy I think.