When a support agent responds to a ticket, remove it from the list of Open tickets. There is no way to tell from the list that an agent or customer has replied. This forces agents to open tickets several times to check for customer responses. Not every support incident can be answered in one email. If it were only that easy. :)
Other than this, and the (multiple email addresses), everything looks great. I was about to work on switching from eTicket but this feature stops us because eTicket has this feature and we have become very accustomed to it, please add it into osTicket! ;)