I found a significant bug in the latest Nextgen 2.0.66: On some sites at least, you can break the site by resetting Nextgen options (going to any page of the site will show the correct url, but actually show the site's homepage html).
Adding in the missing router_param_slug=nggallery makes the site show pages other than the homepage. Adding in correct mvc_template_dirname and mvc_static_dirname options makes it so you can actually see the options settings page for Nextgen on wp-admin... but to actually show galleries on pages you must copy the full serialized array from similar working site.
I hope this issue gets fixed soon - I think I remember hearing of similar behavior in the 1.x Nextgen as well.
Btw is there any documentation on what the options in this ngg_options serialized array are?