Some nice shots there, @balou_panda! I particularly liked the anemone shot at the very beginning.
I picked up a GH4 body about a month ago, with the intention of using it alongside my existing Canon gear. Although there's no way it will replace my Canon body for most stills work, it does have some features which may prove useful for acquiring stills in certain situations, particularly fast action in good light: eg. 4K Photo mode, 12fps RAW, or -- using the electronic shutter -- 40fps jpg.
However, the main reason I selected it was to be able to shoot 4K video with my Canon lenses (I'm using a Metabones Speed Booster), and to shoot slow-motion HD video as you've demonstrated here. I'm editing the 4K footage onto a 1080p timeline, and outputting to HD only, which gives great flexibility to crop in on a 4K shot yet still retain excellent quality. The Speed Booster allows use of image stabilisation on my Canon lenses (useful when handholding, although I try to use a tripod wherever possible), and allows setting of aperture in-camera on these lenses too. It also allows autofocus on the Canon lenses -- although I tend to use manual focus for video work.
I'm a fan of the film or cinematic look, so it's interesting so see it applied to shots in a zoo setting as you've done here. I'm currently experimenting with different menu settings (of which there are many on the GH4!), and getting to grips with profiles, colour correction, grading, luts and all that good stuff!
Perhaps it should be pointed out that, for those happy with more of a 'video' look to their shots, the GH4 is quite capable of providing natural-looking 4K or HD footage straight out of the camera.
It is a great camera, and I'm looking forward to shooting with it during the coming months. Also looking forward to seeing more of your work too!