The biggest changes will be for phones upgrading from Gingerbread to Ice Cream Sandwich, rather than for tablets upgrading from Honeycomb,
as a lot of the new UI features were introduced in Honeycomb.
The UI change is a big difference and brings Honeycomb's Recent Apps button for easier access to multi-tasking to the main-line Android
platform along with the System bar that it sits on.
The standard Lock Screen now has quick access to the Camera and Notifications, and there will be album art and controls for music
playing in the Music app on the lockscreen.
When an incoming call arrives, users can now quickly respond by text message, without needing to pick up the call or unlock the device.
Improved text input and spell-checking on the standard Android 4 keyboard
Android 4.0 introduces a powerful new voice input engine that offers a continuous "open microphone" experience and streaming voice
recognition.
To meet the needs of users with tiered or metered data plans, Android 4.0 adds new controls for managing network data usage.
Enhanc[ing] the accessibility of Android 4.0 for blind or visually impaired users. Most important is a new explore-by-touch mode that
lets users navigate without having to see the screen.
A new People app that offers richer profile information, including a large profile picture, phone numbers, addresses and accounts, status
updates, events, stream items, and a new button for connecting on
integrated social networks.
The user's own contact information is stored in a new "Me" profile, allowing easier sharing with apps and people.
an updated Calendar app brings together personal, work, school, and social agendas.
a new visual voicemail features integrates incoming messages, voice transcriptions, and audio files from one or more providers.
The Camera app includes many new features... continuous focus, zero shutter lag exposure... Stabilized image zoom... users can now take
snapshots at full video resolution just by tapping the screen as video
continues to record... built-in face detection locates faces in the
frame and automatically sets focus... single-motion panorama mode...
Redesigned Gallery app with photo editor
Live Effects for transforming video
instantly sync and manage Google Chrome bookmarks from all ... accounts
Android Beam for NFC-based sharing [requires NFC hardware integrated into the device]
Face Unlock
Wi-Fi Direct lets users connect directly to nearby peer devices over Wi-Fi
built-in support for connecting to Bluetooth Health Device Profile (HDP) devices... users can connect to wireless medical devices and
sensors in hospitals, fitness centers, homes, and elsewhere
