Other then a little sweat around the ears it's very comfortable, but due to the nature of the material hugging around ears despite it being plush and not hurting your skin a little natural perspiration will happen there. You mostly won't feel it at all until you take the headphones off.
So yes, extended gameplay isn't an issue. They're bulky though ( not that you actually feel the weight of it but the size of them is still notable )so "laying down" with them or something like that isn't really an issue. It's meant for having your head essentially upright. Slouching, laying down but head titled up, sitting up in your computer chair, etc. all good postures for extended use.