A really long poem needs meaningful message & substance to merit the length. I personally don't need rhyme. Too " rhymey" can come off as a bit corny like an outfit that's too matchy-matchy. But rythm is necessary to keep me reading. Otherwise you may as well go for a short story, or if you have enough material, a novel.
Too " rhymey" ....I write, I publish, and I post. Rhymes, they are all I do. No matchy-matchy in my work. Wolf Love and Forgiven are long and rhyme. These two works have achieved high marks and literary achievements. I will always defend the ryhme.