Sadly, 'Inside Room 913' didn't manage to float my proverbial boat.
If I had to say why, well, I think it would come down to the following things:
1. No building of intrigue - it's a good premise (a room in a former sanitarium where the resident hasn't been seen for 50 years, but where the food that's left is always eaten), but the main character (Cynthia) becomes almost instantly obsessed by Room 913 without any real basis for being so (yes, we're told she's inquisitive, but the 'need to know' is almost instantaneous from the moment she starts working there - I felt it would have been better if there had been events which piqued her interest and slowly drew her in to investigating Room 913, rather than her immediately jumping in).
2. The re-stating of the protagonists characteristics e.g. Janet's tendency for excessive talking, Cynthia's curious nature, etc. In my humble opinion, such things only need to be stated once by the author, and then maybe occasionally re-iterated. Repetition of such things isn't really needed and slows the narrative.
3. A slightly predictable 'twist' - I'm afraid I suspected that Mr Jacobson was Cynthia's father from quite early in the story. As such, the denouement lacked impact for me.
4. The final chapter - I felt that this went on for too long, providing a series of detailed explanations as to the how and why of Jacobson's actions and his relationship with Cynthia. For me, it would have been much better if this information could have been subtly drip-fed into the narrative in earlier chapters so that the final 'reveal' (Jacobson's one-night-stand with Cynthia's mother) comes right at the very end.
5. Tight editing - the novel would, I suggest, benefit from some aggressive editing to really tighten up the narrative and add an edge to the scenes of tension (such as when Cynthia actually breaks into Room 913).
Of course, other people will no doubt read this book and will enjoy it - that's the nature of opinion. For me, though, it didn't quite hit the mark.