I'll say first off that one of the things I liked about this game is that it never puts you in an unwinnable position (there should be a tag for this, but I'm not sure what to call it); and I'm glad that other reviews told me this, because it made it easier to immerse myself into the mindset of the story.
The tension-building is well-timed, as are the hints - I never felt as though I was off the hook for a moment, and I never felt overly frustrated. I did find the ending slightly confusing; I'll give it another go some time to see if I can make it make more sense.
To give some context here, the main attraction of IF for me is the storytelling - I enjoy the odd puzzle, but not half as much as a well-told story. The storyline of Shrapnel is interesting but not ground-breaking; Shrapnel's strength lies in its medium. The choice of IF over paper and ink pulled me forcefully into a narrative that I might normally have dismissed as "not my thing". Moreover, it's a story that I plan to read again, or at least skim.