Thank you for your answers !
@koraks : yes, I'll keep experimenting. As to adding some "special effects", "collodion style", I've tried in the past, and was never satisfied...
@Donald Qualls : it could indeed just be DOF, although I've never really had that "3D feel" with pictures taken on full frame or even medium format using fast lenses (F/1.2, or even 0.95 for example). Some 6X7 taken with the Pentax 105mm F/2.4 were interesting, but still not really "it". I wonder if the aspect ratio and perspective and, as you mentioned, the tilt movements, don't play a role too... It's really hard to explain. Take 2 examples : when I look at the pictures of one of my favourite photographers, David Burnett, most of my favourite ones are taken with a LF camera (and an Aero Ektar lens, so yes, super shallow DOF). And when I look at this comparison (
), I always choose the LF pictures over the FF ones. There's just something about them. Maybe the lens plays a part too... I really don't know. I just like "the look".
@Ray Morgenweck : thank you for your insight. Yes, it might be that. I had never thought about that...