An important feature lacking for now as far as I know is content/web filtering especially for corporates wishing to block inappropriate/time wasting content like facebook. Addition of this would place it a par with the best like Sonicwall and Fortinet.
At a previous employer, we utilized a Fortigate 200B to replace multiple boxen (two firewalls, barracuda, etc). I found it utterly underpowered for the featureset (even with much of it disabled), and its ability to utilize multiple WAN connections was extremely limited. I realize this is only a low-to-midline example of their lineup, but I was consistently surprised by how easy it was to overwhelm the device, especially given the price-point. The only thing I remember liking was the SSL-VPN functionality, but we couldn't use it because there was no Vista support at the time, so that was disabled too. Now, perhaps they've made progress, or their higher end devices perform better - just sharing my experience with the 200B. Nathan