Just my two cents, after binging the first three seasons.
I was disappointed in the final episode. This was my favorite season, the characters seem to be hitting their stride. So many wonderful moments that make this show unique. I have watched the "Under Pressure" scene multiple times on YouTube. It all seemed to be coming together. Other parts of the finale seemed to work just fine, the Fairy Queen sacrificing for her people, Margo becoming High King and getting her eye back (a FAIRY eye, now), all the hard work on the quest, everything but the climax.
So, in a matter of minutes, we have:
Elliot shoots the monster to save Q (OK, didn't have a problem with that)
Alice makes a deal with the library to siphon off the magic
Alice freaks out and suddenly wants to prevent ALL magic
The monster can take over someone's body
The Dean has made a deal with the library
The douchebag librarian can travel to Blackspire, but Penny 23 couldn't?
Julia is suddenly a God, and just as suddenly she's not
The monster takes over Elliot and sets up the next season
We lose all the keys
We get back all the keys just as quickly
There are potions available to make everyone forget their memories and everyone willingly takes it
I'm sorry, but to me, the finale was a muddled, horrible mess with too many storylines and too many sudden revelations and changes. I like sudden revelations. I like when things turn on a dime. But not so many in the same scene! It seems all smashed together.
I realize characters sometimes do stupid things, but when people have to act stupid to advance the plot, it smacks of lazy writing.
If douchbag librarian can travel to Blackspire, why can't Penny 23 astral project there and do some recon?
Why does Q keep his single serving God power to himself, and piss it away so quickly?
Why didn't he just kill the monster with it?
Why didn't Q ask Ora for some information about the monster?
Why did Q rush to CONFRONT the monster? If the team had immediately used the keys, they all would have magic back.
Why wasn't the team prepared for Alice to act all crazy? She's already revealed she was willing to screw them all over, they should have kept an eye on her.
Why didn't someone use battle magic to stop Alice from casting? She took five minutes ginning up the spell.
Why did Dean Fogg make a deal with the library? He would have had magic back, unregulated by the library, if he had supported the team.
Biggest question of all:
Why did the writers spend most of a season drawing up an incredibly involved and fascinating quest, just to screw up the resolution in the last ten minutes of the episode? Any other kind of ending would have been better.