Unfortunately, the short length of this series worked against it in the end.
Memory Eaters brings up a lot of thought-provoking issues: just how much of who we are is determined by our memories? What happens to our sense of self if we lose some/all of our memories? Can we go on living just as we had been if unimportant memories are taken? What about important ones? And what makes one memory important and another one not? Interesting stuff, right? Unfortunately, these issues are given only passing mention and not developed in any way after being brought up--how could they be in only two volumes?
Setting aside issues of the manhwa's lack of thematic development, the characters and plot in Memory Eaters also get short changed. For example, the poor main character spends most of the manhwa passing out or forgetting things, so she never truly becomes a character who can make decisions or react to things; she ends up feeling more like a doll that has things happen to her rather than making things happen for herself.
Similarly, the relationships between the three characters remains confusing until the final pages of the manhwa: Just who was in love with who? Was the girl in love with Dio? With Ces? Was Dio in love with the girl? Was Ces in love with the girl, or was he in love with Dio? If the relationships weren't meant to be romantic, what were they? Friendship? That needed to be clarified at a very minimum.
The manhwa does at least manage to solve one important central mystery by the end (namely, why the girl kept forgetting things), so if you read it, Memory Eaters won't leave you feeling totally confused as though it got canceled early. Rather, this is just an unfortunately short series that bit off way more than it could chew in two volumes.