There are many "classics" that I didn't like (Seinfeld) or never watched (Everybody Loves Raymond). Others I was a faithful viewer in their day but have no desire to revisit (e.g., The Mary Tyler Moore Show, either of Bob Newhart's shows).
I really loved Seinfeld, and voted for it here. But, it took me quite a while to get into it I recall. For maybe even many seasons, I just never really was all that excited by it. But, at some point a light bulb went on or something for me and I totally fell in love with it and watched it regularly. I think it's an acquired taste. My Grandmother used to completely love Seinfeld too... and used to do the most adorable imitations of some of the characters. It was really endearing.
And, about the Newhart shows... my Mom and I used to love watching the second Newhart show (the one where he was an innkeeper in Vermont) together. We watched it really faithfully and my Mom has since purchased some of the seasons on DVD. I completely missed the first Newhart sitcom... I don't think I've ever even seen a single episode of the first one. But, the Vermont Newhart show definitely seems very dated now.
One interesting thing about Bob Newhart, is that apparently he's Ellen's comedic icon and to a certain degree she models her style after his. I remember she had him on her show once and was sitting in awe of him. It was cute. I really like his dead-pan humor. And, you can sort of see a similarity, in terms of humor-style, with Ellen when you think about it.