"Roughly one free game a month, give or take"
First game on the service is Destiny 2: The Collection, no others announced yet
If you stop paying, you lose access to the games. You regain access if you resubscribe
You will get exclusive store discounts (unknown how much, or if it's store-wide / just certain games)
The Pro tier is the only way to get 4k resolution with 5.1 sound
(the last 2 we already knew about)