It really depends but I think its integral to have appealing characters or visuals in some way. If your visuals are boring and mundane then you have no real reason people should give a fuck about the story so if any games spend dev-time on story with characters that are boring then no gameplay can make up for it. There are plenty of games that are raw mechanics and low visual fidelity but only very few that go for tight engaging gameplay, and if your gameplay can't compete with games that have very good gameplay AND charming visuals then you failed at that too. You have to hyperfocus on gameplay then compete with shit like meatboy or dustforce for platformers which at least have some visual identity over nothing.
Sexy characters can help connect people to the game on a surface level but if you have nothing to back it up, then the characters really need to be interesting to make up for it.

It's as simple as that, nobody who makes unattractive slop ever makes up for it in gameplay either causing a circle of mundanity instead. There needs to be SOME kind of hook, otherwise nobody can out-compete the greats that were able to do both or the indies that got the hyper autistic lockdown on mechanics.