I don't want to sound mean but if you think a movie's theme isn't important then maybe you don't really like movies.

I see films as an experience first and foremost. A film succeeds when it makes you feel the intended emotions.

When it comes to action movies or horrors it's easy enough to tell if they were good for you, but when it comes to more experimental films it gets trickier.

Funny Games isn't exactly what I would call a "fun" film, but it succeeds in making me feel like shit so for me it's a success.

Then again, it's not as easy as making an intentionally shocking film with the intention of shocking the audience.

Themes and craft are very important. The theme of a film is the statement it's trying to make, it's the voice behind the people who made it.

Conversely, some films don't really have a strong theme or any theme at all, but they still stand out due to how they're made, in terms of visual style, entertainment value, technical aspects etc. (a good example of this is 2018's Mandy)

But in the end, films are a subjective matter. The most important thing when you watch them is how much you enjoy them and what they tell you.

Kinda depends on what you mean by "arthouse cinema" in this case.

I remember not liking the first hour at all beyond the visual style but it all being worth for the bombastic second hour.