I attended 7 talks.
My favourite talk by far was hacking the GPG. Brilliant, really: https://media.ccc.de/v/39c3-to-sign-or-not-to-sign-practical...
The "In-house electronics manufacturing from scratch" was a very inspiring talk: https://media.ccc.de/v/39c3-in-house-electronics-manufacturi...
The rest were less good for me personally. Either over-dramatic and shallow (with a sexy-sounding topic) or too procedural in topics I'm not an expert in.