I had heard and read about this game a lot before I played it, so I was expecting the worst as far as unfair puzzles go. In the end I thought that with a few notable exceptions, the game wasn't that hard, though I say that having played Zork and accepted my fate that any Infocom game would likely take a dozen playthroughs before you got close to beating it.
I loved the NPCs and their interactions with you and the environment. I loved that you couldn't just guess the right person as the murderer, that you had to gather evidence as well or you couldn't reach the ultimate ending. This game is ground breaking in introducing mysteries as an IF genre, and for a maiden voyage I think I did a pretty good job. You will need a few hints, but I think you will enjoy it.
(Spoiler - click to show)
It probably goes without saying, but digging around the holes in the rose garden for evidence, and the timing of catching George with an open safe in the hidden closet are the two puzzles that it would have been extremely difficult to solve without hints. Additionally, I think the final collection of evidence you obtain to "win" the game is a little thin when judged by the standards of modern murder mysteries.