I have read Mad Magazine since 1999, and also have many of the collections of older articles, including Mad About the 70s and 80s, Mad About the Movies and more. And unfortunately, I have noticed that the quality has declined over time.
MAD Magazine has a good variety of humor, especially in the recurring features, such as "A Mad Look At," movie satires and "The Lighter Side Of". At times it often shows quite good insight, such as how stereotyped people will never accept contradictory evidence in "You can never win with a bigot" (if Jews don't tip, they're stingy, if they tip well, they do because they're rich). As the previous example shows, MAD does not shy away from controversial subjects or sacred cows, but also doesn't stoop to making jokes in bad taste because they can. The jokes in older articles can sometimes be dated, but if you do a little bit of research, you will get considerably more out of the magazine.
Unfortunately, the magazine has taken a subtle shift over the years from commentary on issues of national and international importance and satire on human nature, to more jokes and articles on celebrities, to the detriment of its overall humor and quality. Many of the newer comic strips, such as "Bitterman" are decidedly lower in quality than some of the older ones, such as "Spy Versus Spy". At times, the political neutrality and constant Accentuate The Negative in movie reviews seems forced. You may find that some of the criticisms of your favorite show or personal beliefs can seem unfair, as I do at times, but while this is a case of personal opinions varying, there have been several cases in which MAD has gotten facts wrong (such as forgetting about a twist at the end of the first X Men movie when complaining about a plot hole in the sequel).
The unfortunate truth is that as many of the old guard retire or pass away, MAD is slowly evolving into a different magazine, one that tries to live up to what came before it and not quite succeeding. However, if you can pick up a collection of older articles, you will find it to be a quite enjoyable and often enlightening social satire.