why isn't this a ten

The vast majority of IMDB's users have poor taste.

Plus, you have people voting it down because of Polanski.

It shouldn't be a 10, more like 11. Simply the best movie I've ever watched, I can't see a single flaw in any aspect of this film, it's a perfect piece of cinema in my opinion.

Lots.

First, it is just stupid. The whole plot and characters are annoying.
Second, it is from Roman Polanski about the time he got into his rape thing.
I remember going to this as a kid with my dad and thinking it was OK, but after
seeing it on TV and thinking about it ... I don't much care for it.

It's easily one of my 5 favorite films, but I've tried to get a few friends and teenagers to watch it and they found it very slow and boring. There's no accounting for taste.

I give it a 9. It ends poorly.

No such thing as a 10.

Should be at least 9.0. I asked about one plot hole on this board, but other than that, it's a perfect movie. Acting-wise, Nicholson was impeccable, Dunaway stunning - her best performance: subtle, elegant, varied. I admire Polanski's instincts to insist on her casting. Likewise direction. And writing! Towne's script is the gold standard of screenwriting. Add to that inspired dialog, design, cinematography, editing - all first-rate to exceptional. Of the scores of movies I love, this is #1.

For me it's a ten.