I'm playing Dark Souls at the moment, and it's hard, but it doesn't seem half as difficult to me as Fifa 15. Trying to play on anything above world class mode seems nigh on impossible for me, and don't even get me started on ultimate team.
Though, I suppose Ultimate Team would be roughly comparable to Dark Souls PVP system, which I've never encountered yet, so I'm not sure if that's rock hard or not.
I'd add the latest football manager games as well, these days it seems that in order to play it you ideally need to have completed your UEFA Pro License.
The thing I love about Dark Souls' difficulty is that as it keeps throwing you at the same level until you complete it, so once you learn and adapt, it gives you the feeling that you're getting better at the game. In Sen's fortress, going from 'Oh, FFS, this is just ridiculous' to zipping back and forward through it like Indiana Jones on my way back to Anor Londo really makes you feel like you've accomplished something.