The thing about freeware games is that it's a very rare thing that they have a story. It's an even rarer thing if that story is something worth even looking at twice. That's very important to me, just blowing people up can be fun for a few minutes, if I can get it to work, but not longer than that, unless it has a story, of any kind. Most commerical fps's have a story, not necessarily good, but it's there, it's a motivation to fight, and it provides acess to the world that everything is happening in.
Since that's why I buy games in the first place, the story and the world, and they are lacking in most, if not all, freeware FPS's I've seen I have to say that the latter kind of sucks. Fun for maybe a few minutes if you have nothing else to do, but not much longer, unless it's REALLY well made.
Another thing is that most such games aren't finished. Freeware producers seem to always release a game when it's at 30% finished or something, and that detracts from the experience as well. The gameplay is often lacking and nothing more than shoot, shoot, shoot, which is often buggy and badly balanced.
Graphics people will also note that the graphics are often worse, which is not something I usually have a problem with, if it's done in a unified style, and everything looks consistent and good (by good I don't mean lots of cool effects that make it look ultra-realistic, I think such games are boring. I mean in the way The curse of monkey Island looks good. Or the way super mario looks good). That isn't the case in the games you've mentioned.
This is not to say I dislike freeware games, not at all, I wouldn't be working on one if that was the case. But there's no reason the quality should suffer, nor is there a reason you should release a buggy half-finished game that looks crap and that has no immersion whatsoever.
