The sarin storyline ended early on in the episode, and the Alison storyline ended abruptly without a final confrontation (and therefore felt unsatisfying). I feel we needed to see her finally admit her guilt to Saul before she died.
I love the character of Quinn but I'm not particularly worried Carrie's going to kill him or she would have done it already. Also, the writers would be mad to kill off the character who, in my opinion, has become the most compelling of the three. However, it is possible Rupert Friend wanted to leave the show, so I'm not taking it for granted Quinn will return.
I enjoyed the season as a whole though (despite some jarring plot holes), and looked forward to it every week. It was a good idea to take it in a new direction and setting, however I think it suffered from keeping the power team of Carrie, Saul and Quinn apart most of the time.