Needs a speed up button. Needs unit select hot keys. Needs a speed up button. Needs key to escape out of current unit being upgraded. Needs a speed up button. Needs to open next unit when clicked in stead of requiring previous unit window to be closed first. Needs a speed up button.
everyone has said things such as powerups, new enemies etc. Another thing that you might consider is the music. Each time it repeats, make it a little higher pitched and faster.
 "Protector"){kind=icon}
 "Dangerous adventure"){kind=icon}
 "New York Shark"){kind=icon}
 "CycloManiacs 2"){kind=icon}
 "Sarah's Run (preview)"){kind=icon}
 "Flight of the Bumblebee: Limp Buzzkit's Journey"){kind=icon}