It's certainly not all bad. The diminished version of Doombolt is actually a good change. The same goes for Black Horror. Within a max 5 dice context, it's sensible to just skip the boosted version... I don't think it was necessary, but it's not that bad.
Also note that IF doesn't make a cast succesful, regardless of the value. So it's more difficult to IF your way to out of reach casting values, which severely limits the benefit of IF... not that it would be a tactic I'd appreciate in the old edition.
Chillwind certainly became more usable. Perhaps even usable
Soulstealer is a strange beast. It had a workable dynamic in the 7th ed book. In the 8th edition they made it a mess and the spell usually wasn't worth the hassle:
Cast roll -> dispel roll -> template -> scatter -> determine hits -> roll to wound -> roll ward -> roll for healing -> roll wounds for spiteful conjuration .. urgh.
Way, way too much work for something as underwhelming as a S2 hit. I'm glad they had a look at that spell. But then they removed the 1 roll I think they should have kept. With Power of Darkness easily adding a wound, that Soulstealer was a fun compensation. With the power dice generation being limited as it is, power of darkness is even more of a gamble. Without Soul Stealer to help out, I predict PoD is going to drop in use considerably. Keep in mind, that at best you can generate 3 dice total, channeling included. It's quite possible you're stuck to 1-2 dice generation max, which is getting awfully cramped with channeling and other means to generate PD.
While I think it's a good thing they limited some of the excesses (nobody wants a 10-3 dice magic phase), the reaction they took seems to me like "they hated something alright". Almost seems to be written by Dwarfs
Note that they didn't lower the cast value of PoD, didn't improve the utility, and so by game design they pretty much nuked down another spell that was already struggling.
It's a signature spell, and with Doombolt still being good, it doesn't affect the Lore as much. But it's hardly an improvement.
The nerf to Warlocks is a welcome one. I don't recall ever using them and not feeling a little dirty. I would have kept their point cost and reduced their ward save from 4++ to 5++... But at 30 points a pop, they are still good but a bit expensive to make a bus from. Works for me.
The pegasi, well... I guess the problem they were trying to fight is the excessive spamming of them. Some lists would carry half a dozen. Considering the utility they add to our army, though, I think we may still see one or two in some lists. I can live with that, if it makes the game more balanced.