Personally I think all video games are a type of art. It's art with a function (to entertain), rather than fine art. Much in the way that film is. Well, most film. But since we're talking about the unfortunately named sub-genre of "art games" then I guess I'll throw my opinion into the mix:
Some are better than others but in general I'm not a fan. I tend to think of games as "fun" and "challenging." Fun technically isn't a necessary component for games, but it's widely accepted that interaction, challenge, and goals are. Many art games are lacking in one or more, and so don't really meet my own personal criteria for what makes a game a game.
But that doesn't mean they're bad. I just personally don't like the actual playing of them because they tend to be boring as hell, as far as interactivity goes. I agree with your assessment that art games are more art than game. Most art games that I've played have no real gameplay to speak of. They may have rich emotional messages (or not) but in my opinion there are better mediums in which to express your ideas that don't involve attempting to tack on a bare minimum of interactivity that ultimately has no bearing on the message or experience.
I have yet to see any art game that I thought wouldn't be better suited as a short film, or a piece of music, or a written poem or story. But then again it's not for me to say what medium the artist should be using to create his work, now is it?
I would say that when you're making a game, it's already art. It's born of your creative process. And if you're making an "art game," then be sure to include the game part of that. Just my own personal manifesto, I guess... keep the game in your game.
And before this thread runs headlong into another argument about art games I'd like to remind people to remain civil, that everyone is entitled to their own opinion, and no I don't expect everyone to subscribe to mine