I would say all games are an artform in themselves The only thing that changes is the style, as with any other medium.
First, I think the definition of art is something that needs to be understood a bit. Okay. To a degree, everything is art. A teacup made by a silversmith, even if plain is still a form of art. It is art as a craft. Basically every human creation can fall under this to some degree or another.
See, here's why I say "there are as many answers to this question as there are works of art."
Your definition of craft as art is arguable. When I was at the Art Institute, one class tried classifying fine art as "something man-made that is neither trash, nor tool, nor craft." (Craft being separate from art because craft has a functional purpose as well as an aesthetic purpose.) It's a very basic, and very ambiguous definition. Especially when you realize that even a hammer can be art if you hang it on a wall and your name is Marcel Duchamp.
Rather than trying to set a specific definition, or even a set of guidelines, for what constitutes art, you should instead hold up any prospective work of art and judge it on it's own merit.
In other words, instead of asking "what is art?" you should ask "is this art?"
As for the distinction between art and artform... well, I suppose games could be considered an artform, in the sense that drawing is an artform (some drawing is art, but not all drawing is art.) At least, games are in the process of becoming a viable artform. It has to do largely with public perception.
Whether or not a game is art, or is merely artistic is something that must be decided. And there is an important distinction there. If I draw a stick figure on a napkin, it's not art, it is simply artistic. It has certain elements of art. I would say that every game is artistic, but only a few are actually art. In my opinion SotC is art, whereas RE4 is merely artistic (though it was a damn fun game).