From NSIS Wiki
Modern User Interface
NSIS 2 includes a new Modern UI, like the wizards of recent Windows version. This new interface has a lot of features to make your installer more user friendly and can be customed with your own graphics. See the screenshots...
With the new language files and strings, you can include multiple languages in one installer. More than 35 translations are already available.
Easy plug-in system
Using plug-ins has never been easier. For example, downloading a file only requires a single line of code.
New wizard page system
The new page system allows you to add new wizard pages with custom elements. You can also display or skip steps of the wizard based on user input.
The new LZMA compression method often gives 20% better results than the BZip2 compression method.
Named user variables
You can declare as many names variables as you want, like $MYVAR.
Customizable user interface
The complete dialogs of the interface can be customized, colors and backgrounds can be changed, graphics can be added and more...