Master's degrees can be completed in one or two years. They require coursework (commonly 24-30 credit hours) and a thesis, exam, or project. Some programs also have a foreign language requirement, which can usually be met by taking a language class.
Master's programs are sometimes offered at "comprehensive" universities that do not grant doctorates. Some such programs are very well structured and supportive. However, many of your courses will probably be "slash" courses, i.e., taken together with undergraduates. In this respect, your graduate work may be quantitatively but not qualitatively different from your undergraduate work. These risks diminish if the department has a large pool of graduate students and frequently offers graduate seminars.
Master's programs are also offered at research universities that grant doctorates. In some of these programs, you may get treated like a second-class citizen (vis a vis the Ph.D. students). However, you will probably have better resources, more opportunities, and more challenging classes than you would at a comprehensive university. If the school is reputable, your degree will also carry greater weight.