According to the post on Gmail blog, here is what you get:
Reminders stick around – If a reminder isn’t completed, it will appear at the top of your calendar until you mark it done.
Reminders work across Google – Reminders you create in Inbox, Keep, and the Google app will also show in Google Calendar.
Reminders sync with mobile – Reminders created in mobile show up on the web and vice versa. So you can stay on track from just about anywhere.
I am especially intrigued by the integration of Keep. I gotta go check it out.