Janis Joplin does not have one of my favorite voices, and in general it bugs me because it's so wiped out -- "whiskey voice" I've heard it called -- but I also understand why many people love it. She sings with a lot of soul. She pours her heart into it. Same reason I love Louis Armstrong's "What a Wonderful World". His voice actually bothers me, actively, but the song is so great and there's so much passion in his voice that I still enjoy the performance.
I have to be in the right mood, but every once in a while, I like Janis Joplin. Also, the guitar work on this song is pretty tasty.