I have been using and customizing a couple of Gallery2 installations at work and in my personal life. I have to say that I am extremely impressed at how advanced and powerful the application really is.
The installer is probably the easiest (besides WordPress) installation I’ve ever performed. All I had to do was download a small starter package, add a password and upload it to the correct directory. From there, the installer transferred all of the necessary files from Gallery’s server over to mine and gave me very explicit instructions on how to configure all of the settings.