Well, I'd rather would have preferred kind of an "open arch". To me, during the 4th season, WW was trying to quit and reedem himself ; at the end, it seemed that he woukd be able to. Nevertheless, I enjoyed the 5th season, but... he deserved better (story wise)
Did he though? The entire premise of the show is that he really isn't a good person and all his problems are self inflicted due to his arrogance and pride. I really think he deserved exactly what happened to him.
I've always perceived him as a desperate man that got more and more dehumanized, until, well... found someone truly bad, but not as a bad person himself. But you have a point, he put in such position due to his arrogance.
The thing is, his desperation is entirely of his own making. He was offered enough money and support to get by with no problems in the first episode, but turned it down because he was too proud. He put his family through everything in the show entirely because of his pride, all while saying he was doing it for them. I'd argue he was a bad person from day one.
It was the fall of Walter White. If we ended at series 4 he's a successful drug dealer and no moral lesson was learned. Series 5 saw his greed lead to his downfall and eventual demise turning the story into a tragedy.
IIRC, he was a successful drug dealer, but wanted to quit, and at the end of the 4th season it seemed it was what would happen. Anyway, as I said before, I enjoyed the last season, but the (more or less) open ending of the 4th wouldn't have been bad (IMO)