Would "Η περιπέτεια είναι ενδιαφέρον" be acceptable?
No. The adjective is "ενδιαφέρων", "ενδιαφέρουσα", "ενδιαφέρον". Although most people tend to use the masculine or the neuter form for all genders, the correct form for feminine words is "ενδιαφέρουσα". :-)
Wonderful! I have been worrying about this difference too. We need to get the ο η ω distinction right in the spelling too, do we?
I think it will be still marked correct if you miss it, but it's better not to xD