That moment when Corypheus strides out of the burning rubble of Haven for the first time I felt a chill, because boy howdy did I remember fighting him in DA2. He had such potential to be an awesome villain, but it really wasn't given to us in DAI. He became such a cheesy "meh, who cares, I got elfroot to harvest" type of non-threat. What I find most sad about that is he really could be a tragic/sympathetic character if you had the option to learn more, and not everyone did. I find his concept fascinating. I wonder how he would have turned out if DAI had really been double the length like they originally said it was. 
Which, come to think of it, I also wonder how things will work if they move Solas forward to DA4 with a new protagonist and someone new to the series starts playing with that game. They're going to miss a lot of context, moreso than people who started with DAI and didn't get any of the Dalish background of Fen'Harel to begin with. I certainly hope they wrap up some of those loose ends with the Inquisitor and not a new person. It would be a bit shaky then.
Yes. (Obviously I'm a bit partial to Cory). But I think the magisters overall were incredibly tragic and when you read the WoT2 you find that he - Cory - really was a deeply religious person. It was not power he wanted perse. He wanted affirmation. What a powerful story to weave in with what's going on with Solas and the rest of the pantheon. Man facing God.
Which was not conveyed appropriately in-game. I'm fine with wiki's for background. I'm fien for random fleshing out of characters -- like supplemental comics that go over their history(like Cassandra and Regalyan). But to need that to actually tell the story they wanted to tell -- and with Cory THAT was the story they wanted to tell -- it shouldn't be necessary. Again, it was a mis-step. This game was far from pefect. It shows where they bit off more than they could chew. But not atrocious. They have a lot of interesting lore. They just need to be better about implementing it.
This story really was abotu the elf/human - and mainly about the elf. They could have streamlined it to just have an elf Inquisitor. You ahve that parallel with Ameridan etc. etc. They could have fleshed it out a lot better. As much as I would have loved to play a Cadash/Adaar it was like 'why?'. Another game perhaps. One that focused on what it meant to be a dwarf or a Qunari blah blah. Likely not an opinion that will get me a lot of love, but whatever.
As for a New Protag: I'll leave that to the DLC. If it's not wrapped up well - then yeah I would agree. If it is, then we shall see. It is getting LUDICROUS that Leliana literally meets every important person in this universe.