I was evaluating OpsGenie as a viable alternative to PagerDuty went through the documentation multiple times but could not find options to perform the following actions:
1. Option to unacknowledge an alert after a given interval (say 10 mins) if an alert is acknowledged by someone.
2. Option to disable the notification suppress if someone as seen an alert. There's no concept of seen in Pagerduty.
e.g: If someone has seen an alert, he/she is not notified again.
Both of the above mentioned points are something we use in Pagerduty and is readily available.