I dislike the change to Sunders, they should stay exclusive to Heralds. Being able to find them anywhere is dumb in my opinion.
I really like the herald changes though. The fact that you could go multiple entire acts without seeing a single herald before was ridiculous. After playing the PTR for a while longer, i do think they're a bit too common now though. But I still prefer it over the way it was before by a long shot.
Them popping up where the monster that triggered them was killed pulls me in more the longer i played with the PTR as well. They make you feel actually hunted. You have enough time to move away before it spawns so they don't drop on your head, but they still have a very real aspect of danger now.
You get a message in-game saying you've drawn ire, about a 1-2 second delay and then they spawn a random pack right on top of you or next to you, which could easily instakill people depending what spawned
If its just making a bunch of crappy monsters it won't matter, but t5 heralds with 3.5x damage and 14x minions with 1.5x damage, well that can OHKO people
I don't know what happens if you try to dodge the moment they spawn, and from what I see the vast majority of the time they spawn a reasonable distance from you, its probably the limitations of D2 placing units that makes them go on top of you when they're 'supposed' to be a short distance away
They spawn at the monster you kill that triggers them. Which is usually right on your head if you don't move as soon as the message pops. You can see a light ball where the monsters corpse is(like when you pop a seal in chaos), and after a few seconds they spawn centered on that ball.