I'm trying to work my way through the Infocom catalog, posting my thoughts on a gaming forum all the while.
Deadline was, in its day, a technical marvel. Nothing in Zork I or II could have prepared players for its intricate machinery. The suspects roam the map, living out their respective days, and these people can actually talk about more than one thing! They sometimes alter their schedules based on what the player does. The protagonist can catch them lying by confronting with evidence. They can be tailed or hidden from. You can even send items to a crime lab for analysis. Deadline is, in other words, a game where you get to do cool detective stuff.
The mystery itself is of the locked door kind, a type familiar to anyone who has read a bit of genre fiction. It is rewarding to unravel, too. There are multiple people deserving of the player's suspicion, and multiple playthroughs will likely be required before the player can focus on the killer.
It makes for a type of "groundhog day" effect; the player will have to spend time learning the characters' schedules and narrowing the investigation.
I have heard others say that Deadline is unfair, though I didn't find it so. Much will depend upon the player's actions when discovering a specific clue. Some find the appropriate action unmotivated, while others had no such problems. I have seen competent and experienced players stand on both sides of the fence, so your own experience of Deadline's fairness will likely be idiosyncratic.
It was one of the first Infocom games I played as a boy, but I never solved it then. That would come years later, taking me two years. It was a game I put down and later returned to, again and again. I usually thought of new things to try while in the shower or driving. It's that kind of experience.
Deadline is the first game of its kind. Other games labelled as mysteries really weren't. Not like this.
I don't think that awarding a rating to Deadline would be very productive. It is a foundational work in terms of both story and programming. I'll start rating games with Starcross if/when I get there.