I don't know why people were so mad at Tarantino for his portrayal of Bruce Lee. First, it was Cliff's memory, so it was probably biased towards him. Secondly: as evident by the ending, the movie takes place in an alternate universe. It is entirely possible that in this universe Bruce Lee was a completely different person.
And about the ending: many people find it to be too violent, but I think there is an explanation for it. First off, it is a Quentin Tarantino movie. What else do you expect?
Secondly, I'm pretty sure it's supposed to reflect the brutality of the Tate murders. Tarantino humiliated the murderers in a funny and brutal way, all to make the scene even more satisfying to watch.