That kind of traditionalist can still be found (even here, as we know) but isn't taken seriously by anyone who actually reads much poetry. Coleridge and Tennyson both wrote stirring blank verse as well as formal poems.

In terms of complexity, though, it's hard to find anything comparable to the "Onegin stanza"--iambic tetrameter with rhyme scheme aBaBccDDeFFeGG, where the lowercase letters represent feminine rhymes (stressed on the penultimate syllable) and the uppercase representing masculine rhymes (stressed on the ultimate syllable).

Imagine writing one of those. Now imagine writing 389 of them that add up to a great novel.