Overall, I enjoyed the first episode of the season - the flashbacks worked for me assuming they build on them as a long-arc character development exposition. I continue to think Buscemi kills it in the role - he projects the right amount of intelligence, instincts, ability to shelve morality and street smarts (came out in several episodes last season). That his physical attributes don't fit the stereotype, but that he is so believable, is a credit to him. He is doing a great job of showing a weariness that wasn't there in the earlier seasons.
I've come to be comfortable with the "stay with us and it will make sense" story telling style of the writers / directors. I used to get frustrated when something seemed to come out of no where, but now I know it will make sense if I just follow along. I can't wait to see where they take Chalky this season. He can say more with his eyes than most actors can do with a page of dialogue.
Lastly, the show's period sets and details are absolutely gorgeous. They have not slipped at all in five seasons (as a lot of shows do with details, etc. as they get older). Sometimes, I have to stop and replay something because I got lost watching a period detail - the scenes in Cuba were ridiculously gorgeous.