I've gotten so used to the unpredictable, brilliant endings to Sanderson books that I was hugely disappointed with this one. At any time in the last 5,000 years they could have turned Odium loose and let the other shards deal with it. Just the threat to turn him loose should have united the shards, even without giving it the second shard.
I admit I don't know all the intricacies that so many posters here are aware of. Nevertheless, my opinion now is that Brandon struggles with the all-powerful, see-all gods' point of view.
I'd like to think this all part of Cultivation's master plan, which we haven't realized yet. Hard to think it could be so short-sighted as to replace stupid Rayse with genius Taravangian, knowing the shard would eventually corrupt.
Other things I don't understand-
Why did Honor go from unspeakable hatred toward Odium to paring up with it in such a short time? Hard to believe Dalinar's brief hosting convinced it to do so.
Why couldn't all the other see-all shards (except Harmony and maybe Autonomy) have seen this possibility and stopped it before it happened?
I suppose once Odium was released from his oath and became Retribution, it was free to vaporize Wit. Why stop there? It could vaporize anyone throughout the Cosmere. Why does it need armies?
How does Honor reconcile his nature with Odium's desire to conquer the galaxy and destroy the rest of the shards? The original agreement was to all stay away from each other.
Why do the other shards need five more books to unite and wipe out Retribution? Actuarily, I'll be dead by the time book 10 is published so I'm not buying anymore of them.