The Hero of Ages was a little bit better than The Well of Ascension, but it disappointed me more deeply, for the simple reason that, when you find the 1st book of a trilogy great, and the 2nd one really bad, that balances each other, so you are waiting for the 3rd to tip the balance. So, even if the 3rd book is better than the 2nd, but you still find it poor, then the balance tips to the negative side, and you have a trilogy with only 1 positive and 2 negatives.
The success of The Final Empire was based on the exceptional world building, the easy yet complex magic system, and mostly to the fast paced and action packed general story ARC. The Hero of Ages was nothing like that. Half of the book was spend either on moral and theological issues, or on the inner struggles of the protagonists. I got sick reading what Kelsier would do and how he inspired them all, how Elend loves Vin but doesn't understand her, but then do (and vice versa), how the protagonists can't deal with more than one aspect of their characters and life, how Sazed didn't want to use his metal minds and believe in a religion, but he needed to, and so on and so forth. If that was only a small part of one book in a trilogy, i would understand it, and even welcome it. But when i had to read about it in 30% of the 2nd book, and in half of the 3rd book, i really got sick of it.
“Somehow, we'll find it. The balance between whom we wish to be and whom we need to be. But for now, we simply have to be satisfied with who we are.”
Of course, there were some positive aspects as well, that kinda balanced my rating. The most important one, is that Sanderson managed to close all of the open threads. And i do mean all of them. You will get not only the answers you seek, but even answers you didn't even had questions about. In most of the modern fantasy series, you will either get a general story that stretches in all of the books (like The Broken Empire by Mark Lawrence), or you will get a general story with smaller arcs, divided in each book, making them able to be stand alones (like Greatcoats by Sebastien DeCastell). Mistborn was a combination of the two. By finishing the first book, of course you had some questions, but you thought you understood the rest. By finishing the third book, you understood that you only knew half of what's going on, and the half of this half were lies.
All in all, i have yet to decide whether i made a good choice by finishing the trilogy against my first decision to stop after the perfect closure provided from the first book. I really liked the story and it's elements (world building, magic, action, politics), and of course Sanderson's writing, but i hated the boring and repetitive topics i mentioned above. I will eventually read the other 3 books in the same universe (taking place some hundred years after the original story), but i don't believe that's going to happen soon.