Here's my 2 cents on the Chosen Three.
It's a shame you kill Ketheric first since he's the only one of the three you can take seriously because he has some gravitas, a zone dedicated to building up his character and motivation and isn't a complete pushover. It seems like they just ran out of steam for the other two so defeating them is pretty anticlimactic (also some of the early concepts for Gortash from the art book look infinitely better than the weird 40 year old emo we got). The story would have been more interesting if it was inversed and Ketheric used you to kill off the other two upstart fools and then fight him over the control of the Elder Brain.
The Absolute as the final boss also kinda falls flat since it's not really a character and more of a plot device used by the Chosen Three throughout the entire game which means that it doesn't really get any characterisation, motivation - you know, the type of stuff that would make the ultimate confrontation more interesting. The Absolute isn't responsible for the situation you're in. It's just sort of in the way. There's no real tension or payoff here with the way the story is set up. The people who were actually responsible for your tadpoling are already dead and you're just dealing with the fallout of their actions. It's like fighting a natural disaster. There's just absolutely no catharsis.
The way the story is written now, the narrative tension peaks at the end of act 2 and then falls off a giant cliff. The slow-burning act 3 never manages to get close to the same heights.
