I've heard from many sources that Bill Gates' keynote at CES wasn't all that good.  One opinion is that is was bad for lack of content.  From The Truth That Dare Not Speak: The CES Keynote Sucked:

The big question is how, in 2008, have we come to a point that Microsoft is so bereft of new ideas and innovation that what was once the most important keynote speech of the year turned out to be a complete dog?

However, having just read Presentation Zen, Garr Reynolds' new book (which I highly recommend,) I have to wonder if it wasn't also the presentation style.  In his book he compares Bill Gates to Steve Jobs and says while they are both great men with good ideas, Steve Jobs wins hands down on his presentation style.  

For a great presentation you need:

• Knowledge.  You have to know your stuff.
• Passion.  If you're not excited, who will be excited listening to you?
• Communication Skills.  You need to be able to talk well in full sentence, tell a story, etc.
• Good delivery mechanisms.  Your visuals (not necessarily just slides) need to support your message.  My favorite quote from Garr Reynolds' book may not be profound, but I think it's one 90% of presenters forget.  "You cannot read and listen at the same time."  Let me repeat, you can not listen and read at the same time.  So if they are reading your slides, they are not listening to you.  If you just wanted them to read, send them the slides.  Or better yet the written article or whitepaper.
• Feedback.  I also think you need to get honest feedback.  In order to improve at anything, you have to know how you are doing.  (That's supposedly why surgeons are some of the best doctors.  They get immediate feedback on whether it worked or not.)  I rarely get much feedback when I give a talk in public so I try to give it a few times to friendly audiences and request feedback. It's not always possible, but it does help.

What do you think makes a great presentation?