Be careful not to burn yourself out. It sounds like what you're experiencing is perhaps your first major burnout.
Usually this happens when it's become a habit to work and you aren't getting what you need from it. It may even be that you're focusing too much on only the one project creatively. I know I have to have several things to work on, or else I become easily burnt out.
It can even help to let yourself experiment and get out of your comfortable habits a little bit. Don't be afraid to reward yourself.
All that aside, as artists we are often our own harshest critics. It is important to continue developing ourselves and our skills, our styles, and our expression. However, it is just as important to learn to accept what we've done, to make peace with it, to be satisfied with it, and to continue forward. You are good enough, and you'll improve steadily as you go. Don't force it where it won't come, remember to rest and let yourself have fun, and above all, be careful not to burn out. It can take a long while to come back from a major burnout.
Best of luck with it! I know you can get past this. 