The guy directed almost 50 movies, so I doubt even himself likes them all! By the same logic, if you love one of Allen's movies, it's unlikely that you will not find another 5 or 6 you also enjoy.
I watched Before Sunset a few years ago and thought it was very good. There's one really long camera shot in it that I remember being impressed by. I had no idea, though, that there was a prequel or sequel. Thanks Rayray.