Good Session vs. Great Session ?

I'm interested in your feedback - I seem to be spending more and more time presenting at conferences, and less time sitting through other peoples sessions - when I attended conferences like the PDC, TechEd, Windows CE Developers Conference (now the Windows Embedded Developers Conference now that we have CE and XPE) I attended a number of excellent sessions, and a number of really terrible sessions - there are some really, really good speakers out there, people like Don Box, Martin Gudgin, Marcus Perryman, and others not so great - so here's the question, what makes for a great session, is it ton's of demos, humor and relaxed speaking style, audience participation, small number of powerpoint slides, and more code samples, or all of the above.... ?

I'd be interested in your comments.

- Mike