So just what was Belial's plan there?

[Elric of Grans]

As a rebuttal to the suggestion that the Nephalim singularly resists Belial's powers, we also see that your companions (who are human) are also able to see straight through him. He is just transparent, end of story. Belial's initial plans in Khejistan are apparently non-existent and make no sense. What he does after that, however, does make sense. He learns of the Black Soulstone and sends his minions off to destroy it. Failing that, he is also trying to use you to bring it to him so he can do it yourself. Taking a bet each way is pretty smart, really. Unfortunately, nobody is fooled by this because rather than trying for a `ah-ha, fooled you' twist, they made the whole thing obvious from the beginning. Cool concept, poor execution.

Azmodan would be 100% better if he never opened his mouth. The only flaw with him is his Bond villain approach. If you removed that, you would see someone who sent forth an army that would have effortlessly crushed the world had you not intervened. Adria also told you the secret to how to defeat him, furthering her own plans; had she not intervened, you would not have known of the Sin Hearts and would not have weakened Azmodan prior to facing him. This act is brilliant so long as you skip past Azmodan's mocking.

Diablo is also pathetic, purely because of the mocking. Why? He acts like a 10 year old child, not some terrifying being of ancient evil.

In my opinion, the biggest question is why the smallest and weakest enemies are in fact the most powerful. Seriously, what is harder to fight: Diablo, or a pack of Spiderling Champions? The lore even says Spiderlings are weak nuff-nuffs, but hey are *way* harder to fight than the adult spiders! Fast/Illusionist Spiderlings? The other two attributes are already irrelevant!