Good

Smaller than my smartphone in most dimensions (but thicker) - easily fits into pockets
Battery lasts multiple days
Drastically lower latency on voice calls than the smartphone
Plays music
Group SMS support
Calendar with reminders
FM Radio
Connects to WiFi
Call quality is excellent
Can act as hotspot
Modern web browser with JavaScript
Email client
Basic calculator
Conversation starter: nearly everyone who sees it wants to tell me about a fond memory of a featurephone they once used

So-so

Camera works fine
Group SMS displays a blank subject before every message
Google Maps
- It works!
- It tracks your position on the map
- You have to manually move to the next leg of each trip
- No "location sharing", people can't see where you are, and you can't see where they are
Google Calendar Sync
QR Code Reader in store (has ads)
Podcast app in store (has ads)
MMS (group texts, or photos) can take a few minutes to arrive when the phone is closed. This may be a power saving issue.

Headphone jack doesn't detect speakers, only headphones
No way to automatically mute sounds during "quiet hours" (like, when you are asleep)
Predictive text input guesses one 4 means "g", not "I"
Will not play FLAC files
"Battery Full" notification can't be disabled