But first of all, I'm happy to announce that as of yesterday, this new installer will be the one and only Opera installer. The classic installer and the MSI installer are discontinued, with the exception of MSI autoupdate packages that will still be provided for a while to make people able to update from versions prior to 11.
To put it simply, those of you who dislike MSI won't have to deal with it anymore. For those of you who used the classic installer, we will make sure that you don't miss anything with the new installer.

How it works, in short
One of the main issues we had with both the classic and MSI installer was that, since they were 3rd party tools, we didn't have complete control over their workings, which made it difficult or even impossible to solve some problems.
As a consequence, we decided to write this new installer entirely from the beginning, which now allows us to have integral control over what it does and also allows us to optimize its speed. To make the task faster and easier, the installer code is embedded in the browser code, which allows us to reuse code we already use in the browser.

We are still left with one third-party tool, 7-zip, which we need to bundle the opera package in a single self-extractable file, which is the file you download. When it is run, it simply unpacks everything in a temporary folder and starts up opera in installer mode. For those of you with 7-zip installed, you can actually just extract opera wherever you want and run it.

The user interface
The new installer has a user interface that is functionally similar to the one the MSI provided, with a few differences.
When starting the installer, you should have a progress bar going on while the content of the archive is extracted, then the first page of the wizard should be displayed, from which you have the opportunity to click options before continuing. Once you approve the installation, another progress bar will be shown while the installation is performed. Once that progress bar is filled, the installer wizard will close down and the installed Opera will be launched.

Also, if you happen to install to a folder where a previous version of Opera was installed with either the classic or the MSI installer, the new installer will first trigger the uninstallation of the old version before installing in its place.

The content of the Options page is what you've been used to with the previous installers, with the exception of the "Install For" drop down.
The two first options in that drop down: "All users" and "Just me" have the same meaning as they do in most installers. Both of them will install opera normally and "All Users" will set up shortcuts and file associations for all users on the system while "Just Me" will create shortcuts and set file associations only for the current running user. Also, the "Just Me" option allows you to install without administrator privileges if you actually choose an installation folder you have write access to.
The last option: "External device" is meant for installing on USB keys and similar devices. It works by only copying the files to the destination without touching anything else on the system. It also sets up opera to read its profile from the installation folder. Because of this, you can also use this option to test an opera build without making any change to your system.

Also, this installer does not and will not offer a "Single User" option from the user interface, since it makes little sense to use on Windows Vista or 7 and can actually cause trouble. The closest you can get to it is by selecting "External device". If you really need this setting, you can still get to it by installing from the command line

Command line options

When launching the installer from the command line, you have a number of options available:

• /installfolder <folder> : Where to install. This will be reflected in the wizard.
• /silent : Skips the wizard and installs directly, using the options set on the command line

The following options are currently only working in Silent mode:

• /copyonly : Only copies the files to the installation folder and does *nothing* else. All other options are ignored, except /singleprofile
• /allusers : If used, shortcuts will be created in the common profile folders and registry changes will be done on HKEY_LOCAL_MACHINE (system wide). Otherwise, shortcuts are created in the user profile folders and registry changes will only touch HKEY_CURRENT_USER.
• /singleprofile : Writes operaprefs_default.ini to specify that the profile folder is to be created/found under the installation folder (previously called single user).
• /setdefaultbrowser : Sets opera as the default browser once the installation has completed.
• /startmenushortcut : Don't create a start menu shortcut.
• /desktopshortcut : Don't create a desktop shortcut.
• /quicklaunchshortcut : Don't create a quick launch shortcut.
• /launchopera : Launches Opera once the installation has completed.

UPDATE: Now all the switches of this second list take 0 or 1 as argument. So, f.ex, use /silent /singleprofile 1 /launchopera 0 for installing silently with single profile and without launching opera once the installation is done

UPDATE 2: I forgot to mention in the previous update that the shortcut options have lost their "no" prefix and (obviously) did the opposite of what they did before. Shortcuts are still created if you don't specify the options

With this, I've covered most of what there is to know about the new installer. There are of course a few bugs and issues left to iron out, but ultimately, we hope it will make it feel easier, faster and safer for everyone to get Opera installed. All feedback is of course welcome and appreciated.

Enjoy!