Really only you can decide. You should know yourself well enough to decide on your own if you're blinded to your own work, or if you can reasonably grasp it.
I'm really good about telling whether or not my writing sucks or not. Given, as I evolve eventually I look back on reading I'd thought was great and I hate it. But I think that's a common enough problem, even amongst very successful authors who have thousands of adoring fans.
Really, you should be your own best audience, if you have the mind to do it. If you can seriously read your novel and enjoy the hell out of it, to the point that you'd be willing to dump 30 bucks on it to purchase a copy... then you're on to something.
Other readers are swell and necessary to a point, but for simply deciding the quality of your own writing, you should really just decide if you like it. If you know it needs work, then work on it.
