There are lots of reviews of the new Fantastical 2 for Mac, but Federico Viticci's and David Sparks's cover pretty much anything you need to know. The original Fantastical for Mac was "just" a menu bar app. Even so, it has easily been my most-used calendar interface the last two-plus years because it makes entering events and reminders so effortless. (Quick tip: Use
⌘K to toggle between events and reminders while in the event entry field.)
At first I was meh to the new full-window version of Fantastical 2. I mean, I already have that in Calendar.app, right? But in the short time I've had Fantastical 2 installed, I can say I really like the agenda/month combo in a single view. It's nice being able to visualize a full month or week for time-blocking purposes while still seeing a linear agenda on the left side. Having Fantastical's legendary natural language field right at hand in the same window is great, too.
I can see how any third-party calendar would be a tough sell for most people since the built in Mac Calendar is pretty good and familiar. But I really think calendars are the most important productivity tools there are. In fact, I would say knowing how to really use a calendar is more important than any task management system. I'm totally willing to buy anything that helps me understand and manage my time.
Right now I just can't think of a better way to make a desktop calendar app than Fantastical 2.