The thing that really stands out to me about ICS is the focus on user experience. Duarte seems to have addressed all the little complaints I've always had, and some I never realized I had.
* Moving away from long-presses.
* More consistent app navigation via swipes.
* More usable but still powerful task management/switching.
* Better representation of useful data like contacts and calendars.
* Order of magnitude better camera app, faster, cleaner, with extremely easy sharing built in.
Apparently the UI is finally hardware accelerated as well (though apps have to opt-in), so hopefully it means an end to Android's historically jittery interface.
* Moving away from long-presses.
* More consistent app navigation via swipes.
* More usable but still powerful task management/switching.
* Better representation of useful data like contacts and calendars.
* Order of magnitude better camera app, faster, cleaner, with extremely easy sharing built in.
Apparently the UI is finally hardware accelerated as well (though apps have to opt-in), so hopefully it means an end to Android's historically jittery interface.