I you are having second thoughts about it, perhaps it is time to take a break. Working a year or so on one story burns most people out on it. Take a few days to read some other stories, or watch a few movies. Friends are good too. No writer should be without friends. The main point behind this is if you are having doubts on it, set it down and come back to it later. You'll have a fresh view point and you'll be ready to write again.
If you finally decide you don't want to stop, you can always beat the living hell out of it with the editor's stick. Y'know, things like grammar and syntax, plot holes, or just parts that aren't needed.