I was very pleased with how the Odium thing turned out. Taravangian had been built up right from the beginning as a fascinating, ruthless, utterly driven villain with understandable goals and a bizarre affliction. We saw from him everything I love to see in a complex villain: moments of triumph, unconscionable depravities, humanising affection, personal virtues, fatal flaws, moments of weakness, deep introspection. Even a genuine friendship with his heroic counterpart, whose morals and philosophy are incompatible with his own. Good rust. Great writing.
He was hamstrung only by his place in the narrative, as the expendable, second fiddle antagonist next to Rayse... who was far less interesting (the kill!destroy!death! flavour of evil god) while being infinitely more powerful. Odium's characterisation in general throughout OB was one of the low points of the series for me, as he stood out as a fairly uninspired dark lord archetype (he put me in mind of the Dark One from WoT, only with Voldemort's glib charm and sneery personality) in a cast otherwise brimming with flavour and uniqueness. I really disliked seeing Rayse divest T of all his intrigues and resources and just kick him into total subservience, as it felt like the more compelling antagonist was being sacrificed by the meta need to have a god-level character present the foremost threat to Roshar.
So, the bait and switch here -- Rayse being taken out in an abrupt, shocking way and supplanted by the dark horse villain whose journey we've all been following since book 1 -- is quite fitting to me, and bodes well for the second half of the story.