Boyarsky was brought aboard to work on the game back in 06 when development was rebooted and they had completely different aspirations of making it more of a robust "RPG" with C&C and such, hence why they hired him. Those initial ideas didn't pan out and so he was more or less left to spin his wheels there, which he himself has admitted in interviews since then. There's hardly anything egregiously bad about the worldbuilding and other narrative fluff in Diablo 3 i.e. the stuff he was left in charge of anyhow. The real issues lie in the core narrative and its writing which can obviously be blamed upon the director (Jay Wilson), story lead (Chris Metzen) and co-writer (Flint Dille), a guy whose prior credits consist of saturday morning cartoons by the way.
What, did you not like being called "NEPHALEM" every 5 minutes and how awesome you are? Or that the Lord of Lies was so obvious you immediatly realize it was him when he appears in front of you in the guise of the child emperor? Or that the supposed great strategist demon Asmodan was thwarted easily by you because he could not stop blabbing how he will own you? Or realize that that Adria will betray you right away? Curious! Do you not have a phone?!
Oh I really really enjoyed it, one of my most loved aspects of the game right alongside the incredible itemization and the auction house. In fact my favorite part about Diablo 3's
stellar plot is what they did with Tyrael. And I mean besides the obvious fact that they took his peculiar & marketable design and, in more ways than one, turned him into some plain ass nigga. All his actions and decisions are
really really well thought out in regards to his character and the story overall. First things first he opts to become a mortal instead of just bailing to help humanity like he's done prior, which makes him fall from heaven like a meteor onto Tristram of all places cuz MEMBER DIABLO 1? As a result the dead awaken, the wildlife go nuts, demons run amok, all sorts of turmoil takes place due to him and on top of all that he's conked out with amnesia at the bottom of a pit. Brilliant move am I right.
Eventually mr/mrs playerchar makes their way there thanks to the shitshow he's caused and sets out to restore his memory by way of gathering up his shattered mcguffin sword. Which characters like Rita Repulsa specify is super-duper powerful & important (that thing did blow up the worldstone after all), so much so that it becomes completely irrelevant after this narrative tangent, but nevermind that! Deckard Cain ends up getting killed by Rita Repulsa's butterfly magic during the thrilling fetchquest, yet another casualty that Tyrael is most definitely not directly responsible for. I'm gonna stop myself here before this turns into a logorrheic nightmare. His
abject acts of moronery brilliant decisions are the cause behind almost everything of note that takes place during the story, the whole thing culminating with him oh-so deservedly becoming heaven's new aspect of WISDOM. Naturally his next
wise decision sets the events of the expansion in motion, by the end of which most of humanity's genocided and the big bad evils are at large again. Oopsie poopsie!
What can I say, Tyrael was very well written, same goes for the rest of the plot.