This discussion is really interesting and I agree with most the answers.
However, I'm surprised that no one mentionned (or I missed it) Anamorphic lenses (adapters in fact). Indeed, it DOES create "film-look" and I'd say that it's the kind of image that I've been looking for a while. Moreover, GH4 (with its M4/3 sensor + recent update) is really made for it. You can try lenses like SLR Magic Anamorphot as it's a modern version of anamorphic (easy to use & setup) but it's "only" x1.33 so lots of fan say that it's not enough (x1.5 is better, etc but it costs). Anyway you should have a look on it.
Having said that, I come back to "lens discussion" and confirm that this the thing on which you have to mainly focus (ha) if you're looking for film-look. Some lenses are way better than other for that.
And I'll summarize that "film-look" is possible on GH4 by paying attention to, or getting, the following :
- Good lighting / expose carefully (+ white balance)
- Fast lenses (1.8 or 1.4 and more if possible)
- Anamorphic adapter (not mandatory but really aimed for...)
- Speedbooster in order to get S35 look + more light & bokeh
- CineD (-5 except tone) + 24p + all "i-stuffs" turned off
- ND variable Filter (take great brands like Tiffen or Haida)
- Spend a lot of time on Color Correction (use LUT's and, if possible, DaVinci)...THIS is REALLY important !
Based on that, here are some examples with 4 of the videos that I made with GH4 + 12-35 (+ Speedbooster & Canon 70-200 F2.8 on 3 of them), all filmed in CineD :
I'm now focusing on Anamorphic adapter in order to continue my search of Film-Look ;)