Memoria improves on almost all of its predecessor's aspects, delivers a strong, original and thought-provoking story, a unity of effect that would make Edgar Allan Poe proud, and features some good puzzles, terrific characters, excellent voice acting and beautiful art. It's a bit of a shame that Geron and Nuri, the characters of the previous entry, get second billing, but their story arc gets told to a satisfactory conclusion as they serve as vehicles to tell the story of Sahja, the new protagonist.
The only reason it doesn't get five stars is because of the odd graphical glitch, some dialogue which doesn't correspond to the text and some misplaced sound files that fail to take into account what has already happened (describing objects that are no longer there or have been changed, for instance). And because of what I assume is an infuriating bit of poetic license taken with the English localization in a puzzle, which forced me to use a walkthrough, as I was stumped due to being led to a wrong conclusion. That being said, Memoria is a great point&click adventure with a fantastic story, and it can get four and a half stars, for all I care.
Also, game developers take note: Sahja is how you write a "strong" female character. Not an all-conquering Mary Sue who can do no wrong and can do everything on her own and better than everyone else, but a compelling, fallible character with an actual personality instead of being a gestalt of "badass" traits.