Definitely a gem amongst the recent adventure games.
The game is very old school in a good way. A good solid adventure with a slow pace and investigative take. I found the story to be very good, even the ending(s) that have risen some mixed feelings. I love when they leave some things for yourself to interpret. Usually that kind of games and endings linger in your mind longer and make the experience a lot more memorable.
Graphics are beautiful, voice acting is pretty solid (though I did dislike the main characters accents at first - I played the English spoken version). Unlike some reviewers, I was never bored. I thought the game was excellent in reaching the wanted atmosphere. At more dangerous or exciting moments I felt the tension yet it never seemed like cheap tricks or scares.
Memento Mori is the right length, rather easy but not stupid. And it has a lot of wonderful details I appreciated. The game isn't perfect though, I admit that, and I can understand why people would consider it only as fair but in no way I understand how this game be rated as bad game. With some little tweaking this could have easily been a 9,5-10 game.
For more detailed review I would read sky-ia's as I agreed on that almost perfectly. I almost wasn't going to write mine but the horrible score here forced me to defend this game.