There are many reasons to love Boba Fett but for me it was because he was a mysterious Man With No Name ala Eastwood in Leone's The Dollars Trilogy, he took no guff from Darth Vader and actually talked back to the man in black.
Eastwood
Boba
(I hope these images work) EDIT: They didn't. You'll just have to click them.
The things that made him interesting to me were the very thing sthat were left unsaid by tell-you-twice-Lucas.
Plus he's ubercool looking and (used to be) VERY cool sounding.
His action figure could fly and he had a missile on his back which could spring out and hit you in the eye.
Like much of Star Wars and Empire (ROTJ not so much) he's very lived in. His outfit is dinged up and used, he's a busy man obviously.
His reputation for disintegrating his quarry preceeds him.
He is not a Kiwi and we all know he made it out of the Sarlaac pit.
I really never wanted to know his backstory for sure, and so I still don't.