IMHO, in a scale of value from 1 - 10:
1. Ticket can be created either by mail/ browser
2. Ticket can be assigned to some group mail/personal mail.
3. Ticket can be tracked ,SLAs can be monitored
4. Mail should come when someone responds the ticet.
5. Reports should be available.
6. Customer can do attachment and select priorities.
7. Customers should be created such that different products can be assigned to him for ticket generation for that product
8. Customer can view/get notification on receiving ticket/change of status- NOT ALL But some notifications