Should the slides in a presentation be self-explanatory or be as minimal as possible?

I would say the two most important points are to make slides you are comfortable with and not to limit your oral presentation to reading your slides.

Furthermore, if you are presenting a research paper, i.e., where more written material is available to the audience, then the objective is usually to make people want to read your paper, instead of explaining the entire paper in 20 minutes.

Some people prefer to have full slides, arguing that when members of the audience are not understanding English very well, it can help them to have both the oral presentation and the slides, especially when the speaker does not speak a perfect English. It is also helpful for members of the audience who got distracted at some point, and who can quickly read where the speaker is. Other people prefer minimal slides, arguing that having both the full text and the oral presentation might confuse the audience. In particular, whenever a slide is displayed, the audience tends to read it immediately, and during the reading, to be less receptive of any spoken words.

In other words, the only "bad" presentation would be to have full slides, and to limit your presentation to reading them, because you become basically useless. However, you can have long slides, as long as you consider them as an aid for the audience who haven't followed what you said (for whatever reason), and not as your script to read. You can also minimal slides, containing only the key points. In the end, you need to be comfortable with your slides, and to give a presentation like one you would like to attend.

Matt Might, a rather young professor, has an interesting style, encompassing the minimalistic approach. Have a peek at this video: http://www.youtube.com/watch?v=HaPsYmOmgcI

He also provides some useful guidelines for preparing a presentation: one of the most important is considering your audience: http://matt.might.net/articles/academic-presentation-tips/.

It is important to engage your audience, not necessarily to tell them every piece of information, and, in a way, advertise your work so that they will read your paper.

If you are aiming to get feedback, then you need to focus your story on what you want to get feedback on.

If you are teaching, you will need either more details in your slides or accompanying notes. Perhaps in this case, you might want people to be able to understand your slides without being present. But for regular scientific presentations, I would not aim to make the slides all encompassing. That's what the paper is for.

A slide being self-explanatory? Why would you be presenting then? What's the purpose of YOU being there?

IMHO the slides should enhance your presentation not be the presentation. YOU are the presenter and the slides should help you convey your message better. Having self explanatory slides takes away the attention from you which is a nonstarter for a good presentation. At any given time during your presentation you should aim for having sufficient material on the slide (sometimes just a picture or a formula or at times a couple of bullet points, etc.) to help you convey your message.