Just finished Chapter 1 (playtime 6hrs). The settings, soundtrack, voice acting and pacing are great and really shine. Difficulty shouldn't be an issue for most players (I never used the notebook for help and did not know until 3hrs in that the spacebar shows all active clues in the area (which again I never used)). You can, however, miss a number of achievements on a playthrough and not solve certain "side tasks" as you progress (which happened to me on the train and means I will go back for another playthrough) so if you are a completionist careful attention must be taken and every nook and cranny explored before proceeding.
The game has a few problems, most notably pathing for your character who can take strange routes to reach an object and subsequently can get stuck in the environment. This happened twice on my playthrough. This doesn't sound like a major problem, however, once stuck, the game sticks in a loop and you cannot save or carry out any further actions. As a result I had to terminate the game and roll back to my last save/autosave which could be annoying for some people. I recommend you to save every 15-20mins or so just in case. In addition, the game does have some teleporting issues when transferring to cutscenes and some lip-syncing issues later on. None of these issues are truly game breaking but they do detract from an otherwise high quality experience. One word of warning: the ending is extremely abrupt (indicating that an episodic release was not the original intention) and even though the game feels several times that it is about to finish before it does, you may find yourself watching the credits when you least expect it.
Overall I found it to be a really enjoyable experience, great pacing, soundtrack and settings and an interesting story. Looking forward to chapter 2.
I used the notebook a lot, but more because I was interested in what he wrote about the characters and the portraits, there are a lot of interesting stuff there.