I like Fred! He makes me laugh. He has a great delivery of lines, and I like the fact that he almost always seems to be miserable and/or cranky! I also like the way that he and Ethel put each other down all the time. I love his scenes with Ricky, too.
Basically William Frawley was a terrific professional (drinking aside) who had years of experience in showbusiness, which showed in every scene he did. There's no substitute for that kind of professionalism, and you don't tend to see it these days. Fred's not my favourite character, but I that doesn't mean to say that I don't appreciate him. I think the show was the better for having him around.