Reddit mentions of Moon Knight: Countdown to Dark

There are a lot of answers to this. Moon Knight has had many series since his creation in the late 70's. There are fans who prefer the Classic Moon Knight, fans who prefer the Modern Moon Knight stories, and then people like me who love it all (except the early 90's trash). If you want the classic Moon Knight, which was written by Moon Knights original author, and his defining artist, I recommend the Countdown to Dark TPB. If you like the tone of those, your next step is to go for the Essential Moon Knight's 1, 2, & 3. These will cover the Origin stories, the major villains, the most important story arcs, and has some of the best comic art of the time. Keep in mind, all of these stories were written in the early 80's, and they are a product of their time.

For a more modern Moon Knight story, you really have two good options. You can either try the Huston/Finch Run by getting Moon Knight: The Bottom (and continue to volumes 2-5). They are a decent enough place to start on Moon Knight if you have no background on him. These stories tend to be very dark and very edgy compared to previous Moon Knight stuff.

What most people seem to be doing, however, is starting with the most recent run by Bendis/Maleev. It is titled quite simply Moon Knight This series is pretty self reliant, and seems to be very popular.