How can I describe how hard it is?

If you know polycarbonate, that is a very stiff and rigid plastic. This case is nothing like polycarbonate.

If you know polypropylene, that is a very slippery and flexible plastic. This case is nothing like polypropylene.

This case is somewhere in between. It has a little bit of flex so that it will "snap" into place, and it's soft enough that I can't imagine any way it could damage the N900.

It makes the phone chunkier, but it makes it feel very rugged and well-protected. I'm well pleased. Obviously different people are looking for different things, but at least this is one of the cheaper options so you might want to try it.

Regards,
Roger