Originally Posted by Michael_Russell
If your update is stuck at 48%, like it was for me last night when I got home, right-click on "SiN Episodes: Emergence" in the Steam Games List and pick "Pause Updating."
Wait five seconds.
Right-click on "SiN Episodes: Emergence" and pick "Resume Updating."
It's a glitch in the Steam client that has been reported to Valve.
Mine was stuck at 95% for over 16 hours. I tried pausing and restarting with no go. I then rebooted because of a Windows Security Update and restarted Steam. Still nothing. I eventually had to Delete all Local Content and redownload SiN completely.