For me, the ending is perfect because I was able to see all my favorite characters again and how they got their happy ending peacefully, but it's a very long list that could have been done better.
A few examples:
Azura and the author: I found the books pretty pointless and cheesy. It could have been such a great story - my headcanon is that the author of the books had witches as ancestors who came to the human world and now the author has human ears but still has magic and can use Oracle magic to see into the future, which is why the books are so similar to Luz's story. Just my headcanon and it would be paradoxical but the way it is now it just doesn't work for me.
Luz development: There are really a lot of things that were "lame" but the fact that Luz didn't develop and lives in her "perfect fantasy world" until the end is such a bad plot. She never really got to know the "real" Boiling Isles, it's just her fantasy and she hasn't gone through any development and is still the same "lost" Luz as at the beginning even though she now has friends, a girlfriend and is understood.
And I agree that many characters like Vee, The Collector, Archivists, Titan Trappers etc. deserved more screen time and more story.