Blue, writing is a subjective business. What one person hates, another might fully enjoy. Don't be afraid to tell yourself that so-and-so person, whomever this is that told you your work is rubbish, represents only one opinion.
It's like the saying, "One man's trash is another man's treasure." Don't take a solitary opinion as Gospel Truth where your writing is concerned. I've found that critiques of my own work are generally harsher than the words I get from editors and/or agents when they send me their responses to my submissions. So really, what you need is not so much a site to make you better, as a better outlook.
I know it's hard to see yourself as good. It's hard for a lot of us to. But the truth is, your writing can improve with time and practice. Keep writing, Blue, and keep reading.
But before I go, I will give one site that sticks out in my mind. It is the main site of AW, where they have articles about writing posted that you can read online. The site URL is:
www.absolutewrite.com
Also, if you have favorite authors, I would recommend Googling their names or pen-names, and seeing if they might have a web site of their own. Many times they will give good advice, from their own experience in writing, to aspiring authors. You have to remember, every published writer was once unpublished. For every Stephen King, there is a BlueLucario. For every James D. Macdonald, there is a Sean D. Schaffer. In other words, for every published writer, there is an unpublished writer, wanting to reach up to their level.
So consider that you are only human, and if you want to publish your writing, seek out your favorite writers and learn from them.
--Sean