What kind of features are most important to you in an online web gallery? I'm working on a gallery plugin for wordpress and I'm looking for feature suggestions.

The presentation is template based so it's the core functionality that I'm looking for suggestions with.

What kind of classification and indexing are needed. Such as Categories, Mediums, Subjects, etc.

Would you want to attach support files. Such as linking a photoshop file to a gallery image or still shots to a video file.

Any comments or suggestions would be appreciated.