I did subscribe in order to answer your question. The usual thing that you'll hear is that "it's not that bad, you'll have your Ph. D.". And, might you believe it or not, this is both true and the right ting to hear.
Your advisor has better grasp of what's in the field and the scientific contributions of your work. Trust him. Maybe your thesis won't win you a Nobel prize, but if he's confident it will win you a Ph. D. degree, then this is almost a sure thing.
You tend to compare your work with your own standards or maybe with the wrong people's work (e.g. experienced researchers etc.). Take a broader view of the topic and maybe read some really bad Ph. D. thesis. This will boost your confidence level.
This is not to say that you should lower your own standards, but to get over hopelessness. Then, trust people more experienced than you are (the Ph. D. advisor). And finally, remember that a Ph. D. degree is not there to prove that you are a researcher. It only proves that you are fit to become a researcher. Much more work will be needed.
And... a Ph. D. student is just that: a student. You have your doubts, the name "Ph. D." is quite frightening, but you should keep calm, organize your work, and commit to an effort without desperation.
Stopping the Ph. D. right now, on these grounds, looks for me like a "fuite en avant" (that's French. The best English translation that I did find on the Internet is "unconscious mechanism that causes a person to throw himself/herself into a dreaded danger".) Avoid that and only focus on getting things done.
You are also at a moment of your Ph. D. when much of your work is not yet organized and results might seem inexistent. This is because the work that you did was precisely that: a research work. You did explore many spots, contributions seems lost in the bigger picture, but when you start organizing all those, things will become clearer.
My advice: start writing your results in a document, let's say a draft of your thesis and of your Powerpoint (or LATEX) presentation.
This is of double usefulness:
1) will be helpful to you later, in writing the final version of your thesis
2) the strengths and weaknesses of your work will appear much clearer once you try to integrate your work in an organized presentation. The strengths that you'll see will boost your confidence. The weaknesses are the things you have to address.