yeah Gallery2 is the daddy of galleries.It has loads of modules and SEO power. Unfortunately that also makes it labour a bit if you don't have a spritely server with good MySQL power. An example of G2 in motion is http://www.pureanimegallery.com/main.php To put a CMS around it you can use either Joomla, MODx, or Drupal.
Gallery2 is awesome, but with my blog's gallery at 9000 photos it hogs my server and they shut me down occasionally.
Arles is an excellent gallery creator (digitaldutch.com/arles/) but maybe not what you`re looking for?
I will chime in on Gallery2. In general if you have many images/ photos you need more server resources to begin with. Gallery's add-on plugins give more functionality. I am sure there are more simple light scripts if you just want friends and family to see your photo's.
I think Gallery2 like all other similar scripts are the worst scripts ever created. One of those things that have endless features but you're unable to use any because its way too confusing to just try to figure out where they are. Gallery 2 = junk. Its way easier to code a raw script on your own