Coop, quicklime, "Art" is a pretty generic term, so both of you could be right--Einstein called the stars art, Mozart called music art, and my hairdresser calls my dye job art. Other people call it science, instruments, and hair. That doesn't mean that they can't be just as good at what they do as Einstein, Mozart, and Chadd, my awesome hairdresser. They might simply prefer to look at what they do a different way. Art is WAY too complex to define. It's a personal decision whether or not you consider something "art." I don't consider splatter paint to be "art," but there are plenty of modern museums out there who do!
As for a published novel being the judgement of "good"... I'm going to have to disagree here. I've seen plenty of books that I consider lousy on the shelf. In my mind, the individual reader is the only one who can define if a book is "good"--and that is only their judgement. Another person may think it's "bad," and so it's a "bad" book to them.
One of my favorite trilogies is the cheesiest, most Mary Sue, most poorly written hunk of words I've ever read... but I enjoy it, like a dirty pleasure. I've read it a dozen times! One of my least favorite books begins with the words "Call me Ishmael" and bored me to tears with its deeply philosophical chase of a sea mammal that came off as unrealistic as Jaws. The world considers this a good book, but I don't. I know someone who thinks the Harry Potter books are crap and that the Hunger Games trilogy is laughable. But obviously some people like them, 'cause they sold like crazy. So are they good, because some people like them, or bad because some don't? There's no straight answer to the question "is this a good book?" It's an individual decision and, unlike an election, having more votes on one side or the other doesn't necessarily win the title of "good" or "bad". Take "War and Peace" for example. Literary masters tell us this book is golden... But if you forced all of America to read this book today, do you think it would get more "goods" or "bads"? With our nation's attention span, I'm pretty sure it would be graded as the latter.
In my mind, only you can decide if your book is good. Ask yourself, do I love this book? Even if it never gets published, will I enjoy it ten years from now when I sit down to read it? Is it something I love? Does it make me proud to hand it to my friends? Do I wish there were other books out there like mine?
If the answer is yes, then your book is good and it was worth writing, if only for the joy YOU will get out of reading it. And it may have a chance at getting published, no matter how other people judge it. Hell, some VERY popular books out there (*coughcoughsparklesandfangscoughcough*) would likely have been discouraged by many on this forum. A few people would have loved them and the rest would have said they were unpublishable and needed at least fifteen re-writes. But they got published. Why? Because what they wrote was what that agent or publisher had a taste for at that very moment (or realized their target audience had a taste for them).
My best advice: Worry less about being "good" and write for the joy of writing. I CANNOT guarantee that I will ever be published, but I CAN guarantee that I can write a story good enough for me to enjoy. If nothing else, I will always have that.