1. I don't want to have to press the back button every time I look at a picture (like facebook, for example). To that end, the whole gallery (thumbnails and full size images) should be contained on a single page.
2. I want it to load fast.
3. I want to have it look nice.
4. Each picture should have room for a short description.
5. It should resize to fill the browser window with thumbnails (so you can treat it much like a thumbnails view in Windows Explorer).
Rather than complain about it, though, I thought I'd make something I was satisfied with. Well, I worked with my girlfriend to put one together (She's learning HTML and needed a project). Here's a sample of how it turned out.
Anyways, this post is a heads up, because I wrote a tool to throw galleries like this together, and I'll be posting it soon. More about that when I get there.