What do conference organizers expect from an invited speaker? I am asking this because I am going to be a plenary speaker in a couple of months (this is not going to be my first invited/keynote/plenary talk, but for some reason I never stopped to think about this issue before). I've spent  10 minutes thinking of plenary/keynote speakers I've seen in past conferences, and they roughly divide into two classes: (i) a majority who give a talk that, other than being longer, is pretty much indistinguishable from the talks of speakers that get in through peer-review ("here is a very well-delimited problem, which I propose to solve as follows"); (ii) a minority that attempt to give a loftier, programmatic talk ("recent developments have this overarching theme, which is pointing the field into this direction; here are some remarks on what this means for us all and a sketch of some neat things we can do if we take things seriously"). 

The organizers of this particular conference don't really have a preference either way, but I am wondering if audiences at large do. Personally, I prefer (i), but that is just because I'm more of a problem-solver than a theory-builder.
Here's my take: as a plenary speaker, you will have an audience that is broader than those who may come to a minisymposium or parallel session, and consequently also have a less deep understanding of technical details of your particular field of work. They may also lack an understanding of the motivation for what you are doing: For things in my particular field, I know why people want to do them, but for other areas I often would like to know "why should I care" before I want to hear the details.

Consequently, the talks that I have often found to be a bit boring are those that really are just longer minisymposium talks. The ones I find interesting are those that explain to me the bigger context of a problem: where does it come from, what are the historical connections, were there dead ends in developing solutions, etc. Then show me how you approach the problem and where this leads. I also find it interesting to hear about open problems and ideas for future research -- an invited talk should not just be about the great results of the speaker, but also inspire others to work in this field.