Android 4.0.4 is incremental update of a few hundred changes over 4.0.3.
Changelist:
Noticeably Faster
Android OS bug fixed (in battery stats)
Long-pressing on a blank spot on the last page of app tray bug is gone
New Radios. 3G/4G switching MUCH better. Don't even notice it changing.
Improved signal strength
New Power Menu. New from 4.0.2, familiar to those who have used a stock 4.0.3 rom.
PRIMELA03 Bootloader
Faster boot up time
Auto-brightness Functionality changed. Smooth transition
Holding down camera button now refocuses again
Multitouch issue seems resolved.
Autorotate is faster
Browser performance noticeably improved
Recent apps list opens faster
Miscellaneous camera UI changes
Increased volume
Keyboard fixes
Updated News & Weather app UI
Improved quick controls in browser. New when coming from 4.0.2. Present in 4.0.3.
Source 1,
Source 2 and
Source 3