My experience is that they were nightmarishly hard, punishing even small mistakes with instant death by an AI who seemed to love brutalising you. That said, I've only played the demos/betas for either so I may have a skewed perspective on them.
I think that if you're into hardcore shooters and don't mind them not looking as pretty as the front-running FPS games then this could really work for you. It's clearly targeted at a niche that likes that sort of thing. I'm just not sure I'm in that niche.