The main new feature are a set of new pages, one for each player, and one for each event, displaying the information about those thigns in a way that should work well on mobile devices.
There is now much better navigation between all the different screens, which should require fewer trips back to the main register page in order to get to where you want.
Other minor changes:
The big new feature is support for more than one series of events. This included separating the concept of user from the concept of player. When working with the system, there is always the concept of the current event series, which can be switched using the links underneath the main register.
A smaller new feature is the ability to get a list of email addresses based on the information in the register. For example, you can get a list of all string players who have not yet said whether they will be able to come to the next rehearsal. Naturally, only users with appropriate permissions can access this.
The sort order has been changed to order by firstname, then lastname, rather than ordering by lastname then firstname. That is what the OU orchestra wanted, and it seems more friendly.
Finally, there is a new admin setting. You can give a prefix that is added in front of the name of every event when exporting as iCal. This is so that you can have nice short event names like 'Rehearsal' or 'Concert' in the register, but more comprehensible names like 'Milton Keynes Orchestra Rehearsal' in the export file.