As a starting developer I can say such UI is not intuitive at all. Lot of settings are just hidden and it hard to find them (for ex. the virus chest is under scan settings (well, you can use the tray menu but nobody expected it there I think)).
The icons on the main page is a good decision but there should be more options such as virus chest, update and virus definition & program version info (maybe smth else).
Also it would be great if avast will notify user about scanning USB pen drive when it was plugged in (when I plug my pen drive into laptop it takes some time to scan it and I can't use it during the scan). I found it very useful in Qihoo 360 Total Security.