The investigation part is very fun if the players are into some roleplaying. If you reward them generously with information they can skip a trip back to the start. The final encounter is challenging especially if you don't run the optional part to get some extra help for the party. Somehow the gun is a melee attack in the statblock. Probably this was made to avoid disadvantage in melee but this had the awkward effect that one player would have been punished for dropping on the floor. I recommend treating it differently.