This is not a comprehensive list of the changes (since 1.3beta) but highlights the main points:
Multilingual backend (currently only available in English and German - see Translation Guidance below)
Enhanced user interface
Optional Iconic navigation
Better information in popup messages in calendar - this is also highly customisable
Clearer information when viewing event detail
Highly configurable navigation buttons for mini calendar module
Monthly calendars can now be printed without the whole page being visible
Summary information about event categories can now be shown via the event legend module - by clicking a category name you can easily restrict the events shown in a calendar to a specific category
Easier Administration
Old events can be archived
Old events can be hidden/shown in the list of events
More intuitive layout of event creation/editing pages
Frontend event creation/editing now uses the same interface as the backend
Menu items can now be created to calendars for specific categories (or a number of categories)
Links can be created within event descriptions (via the new event report mambot) - this allows you to create a link to an event report, photo album etc. This link is not shown until a specific date.
Major performance improvements - we estimate the monthly calendar now takes about 60% less time to load!
Most email addresses are now 'cloaked' to reduce the risk of SPAM
Better layout on Safari and Konquerer browsers
Better XHMTL compliance
Year view can now show event repeats if configured appropriately
Introduce the concept of all-day or unspecified time events
Bug Fixes - the list is too long to mention here, please see the tracker for details.