I think a tagging system is a great idea. Funny I wanted to suggest it ages ago (around the time
del.icio.us started) but never got around to it. Are you going to have a nice tag cloud too? Is anyone going to be able to add tags, or just the submitter?
Anyway, I don't think 3d is such a great tag as, like Tom said, 3d can be a bit ambiguous. I think tags like fps or 3rd_person or something would be more detailed. Then again you _can_ have multiple tags so who cares, right?