I've only given talks to small audiences but they were very well-received. I often focus on humour, partially because I don't really have the background to deep-dive technical material hard enough for that to be interesting in-and-of-itself (maybe this is imposter syndrome).

It is very important though. It's very easy to lose an audience, and the truth is a lot of the speakers before you will likely range from slightly boring to extremely boring. The audience can be primed to totally clock out if you don't grab them immediately and keep them for the whole thing.