I'm what you call a newb as well (I registered a while back, but I never posted). But I'm sort of picky. Constructive criticism=low end of mediocre, reasons mainly of the fact that it is just use of the filters and going through the motions. I feel that the smiley one is funny though.
Just so you know, they aren't "bloody potato". I've seen way worse, but I've seen way better as well.
(EDIT: well, if you are new at Paint.NET, these are more than fine)