I'm going to have to throw it in here, I was never a big fan. Reviewing before I wrote this I read that he was originally a cartoonist and perhaps that's the problem. I grew up in the time of the great "underground" comix such as those of R. Crumb, Jay Lynch and Vaughn Bode. While most of the times you will find riotous over-exaggerated characters you'd also come across scenes with purity of line that predates Haring. You'd also find scenes of surrealism and beauty. So when I first began to see Haring's work I pretty much passed it off as the tail end of this movement but made more popular with scenes of family and brotherly love. But I've never seen a full exhibition so perhaps I'm blowing this out of my ass.
My sister, whose a graduate of the Art Institute(and therefore not an artist) was always a fan.
Back to comix for a moment: A knock on them was they were often misogynistic and had other disturbing elements. All of this is explored in what I think is one of the great documentaries of the last 20 years Crumb. Here you have three mentally sick brothers one of whom is saved by art and commercial success.