For what it's worth, Gallery2 is light years above Gallery 1.x. The "one page per picture" thing is solved in a couple of the Gallery2 themes, including the one I use on my Gallery site. Browse one of my albums and you'll see you can do slideshows, use arrow keys to switch images, etc. just like Picasaweb, and it also pulls down the images in the background (though not as fast as Google in my case because of my inferior web hosting.) And, not that it's all that useful,but Gallery2 integrates with Google Maps.

That said, I'd probably be more interested in Picasaweb if I were a Windows user and used Picasa as my photo management app. If they ever come out with an OS X version (I guess the Linux version is in beta, so it can't be that far off) I'll look deeper into Picasaweb. But I would at least give Gallery2 a chance.