The patch is designed to address stability problems with the game and performance issues, however the developers have decided not to change any game logic issues or release a smaller upgrade patch, so the one you're getting is everything rolled into one.
Here is the change list:
- Removed some memory leaks
- Fixed crashes when the game attempted to render lots of content (high detail, high FOV or multiple-monitor modes); this should particularly help multi-monitor users
- Chat window no longer causes lag spikes
- Chat window reworked opacity & visibility-time is controllable through settings in settings.ini
- Clantag is remembered when using auto-login
- Banner URLs can be up to 252 characters in length
- SecuROM wrapper removed from non-Steam version
- Minor performance enhancements
- Reduced rubberbanding on servers with more than 24 active players
- PrintScreen takes a screenshot, file stored in Documents\BFBC2\Screenshots directory
The patch does have some problems when used on a windows login that contains non-English characters (such as ö, ý, etc), the solution to this is to use an account with only characters from the English character set. In other words, "7-bit ASCII only, please".
Ther patch will be applied automatically via Steam or the game auto-updater, a manual version will also be available, details will be on the Battlefield Blog.