I defy you to show me a better looking calendar widget than Month. The material design-style calendar themes (even the free ones) are so gorgeous you'll want to gaze at the year ahead for minutes on end.
The resizable widget adds a touch of class to your home screen. Tap on a date and the background will dim, allowing you to flick through your Google Calendar events with elegant swipe effects.
It's just a shame it doesn't have an agenda widget to show daily events more explicitly at a glance.