Apparently people like long slogs through infinitely spawning trash, from an heretofore unheard of new army - seeing as how the entire point of the game to that point was destroying Cory's armies and power bases - before they get to the final boss.
Who knew.
This is my surprise with people's reaction to the ending. I hate the end of DA:O - I hate that long slog through Denerim. It's the worst. It kept me from replaying the game for a long time and I just "auto-rezzed" my Warden for DA:A at first because I didn't want to re-do that part to have her live (I had saves right at the DR part, so it would only be the scenes before and that battle).
I hate the endings of a lot of older RPGs who have similar end missions that take forever to kill one boss. There were countless games where once the Internet existed I just read about or watched the ending online rather than finish the game completely (I'm looking at you, Final Fantasy X). Before that was widely available, I used to be stuck at the end of RPGs for weeks of non-play before I finished them, if I did.
Now, I do think it feels like there's a mission missing between the Temple and the final fight. It feels like maybe with your "Well of Sorrows" knowledge, you should have done one more quest before facing Cory. This is a minor quibble - but it's the only part where the pacing feels off because you can just go off and dicker around in between (and the only way to explore the Arbor Wilds with any party members you want is to dicker then), but it causes some dissonance because of how the two missions are framed.
Personally, I like how Cory is weakened. He's a force to be reckoned with at Haven because we are unprepared. Then, we get a big, defensible fortress (and those who wanted it attacked - Haven made sense, it was no fortress, but why on Earth would Cory attack Skyhold? How would he do it? He has no access to siege weaponry, especially once he loses his noble support, and even without Skyhold's magical protection, you would need siege weaponry to do so, plus a really large army, right after you've torn his away), which we improve. Then, we take away the two things we know Cory has planned - demon army, Orlais in chaos. Then, we hunt him down and throw our army at his, taking away his lieutenant, and gaining ancient knowledge he wanted. Then, we finally defeat him. To me, the victory feels well-earned after all of that - I don't need or want it in one big, long mission. I like it divided into pieces.
I get that there's no low after Haven, but it always seems weird to me if the low is right before the victory (as why would you emerge victorious right after you were driven low? I get that it happens in stories, but it never makes much sense and too many stories use it). A suicide mission would've been cool in a way (just because ME2 is so cool - it's the only time a long mission felt "good" to me, but that might be because I played it on Casual too), but it's clear that they don't want to account for that level of difference with all the various choices they already have to carry over in Thedas, and I don't blame them.
I don't think it's possible to produce an ending that makes everyone happy, though. I know DA:O didn't make me happy, but I accepted it because so many RPGs had long, sloggish endings back then. Some still do, but I am happy it's falling more out of favor these days.