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.

Examples:
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.
Thanks,
Chris.