While predictable, I thought it was a solid finale. Above someone referenced how it didn't take the "bet you didn't see that coming!" Dexter route, which was terrible, and I have no problem with that.
I liked that Jax went out like his father before him (at least in his mind), with him believing that he was saving children by not exposing them to himself. His goal from the beginning of the series was to change the club into something respectable, and the entire series just shows how he failed miserably and turned into another Clay. Then, because **** happy endings, his creepy kid Able is attached to the ring his grandmother gave him and foreshadows him possibly becoming another Jax. The cycle of violence will continue, and the whole series was for nothing.
That's the kind of unhappy ending I fully approve of, and thought it was a good way to end the series.