I actually found CO's F product to be quite nice, very similar to Delta's if you've ever flown F on them. We flew a very new 737-800 with 18 F seats. They had a few monitors (maybe six?) coming down from the ceiling above the seats and they played a few movies (which actually was very distracting if you were trying to sleep).

We were offered pre-takeoff drinks which I found to be a nice touch.

The seats were comfortable enough (and quite wide). Dinner was good, they passed out menus and even though I wasn't terribly hungry, I could have eaten a lot more than I did. I had some warm primavera pasta thing in a bowl, the courgettes were rather soggy and the sauce bland, but I'm not expecting perfection so that was fine.

All in all, it was a nice flight and an enjoyable experience. If the shameful truth be told, I've never flown NW F before (though I imagine I will soon). As far as comparison to European carriers' intra-Europe C class, I think that domestic F on most US carriers is leagues ahead of most European C products. KLM does have a fighting chance, though, since I've always found their seats very comfortable and food quite good. I'm sure it would be better if there were any time to serve a real meal but unfortunately, AMS seems to be less than an hour from just about anywhere!