Not a notable improvement on Season 4 although at least this has a really strong, emotionally satisfying finale. For most of the running time however this seems to be tap dancing. The kid characters were either undercast or just not evocatively written - Nucky's uninteresting nephew, and the mysterious kid who pops up wanting to be mentored; I kept forgetting who they were. Kelly MacDonald is given something to do but not that much really. You feel like the makers just listed who they wanted to kill off, and let that drive episodes.
Some deaths come as a jolt - Patricia Arquette and Michael Shannon's especially. Chalky's death was moving but didn't make any dramatic sense for me - I know you could argue it, but I didn't buy it, not after everything he'd been through. Michael Shannon again looks lost for a lot of the time, so when he dies, while it's sudden, it's also a bit of a relief because his character never seemed to have direction after he left the FBI. (Which I'm sure was the point it's just not that satisfying to watch).
Eli was just dull here, moping around with three day growth all the time. It was also annoying how the FBI were so ruthless they tortured a Capone accountant into informing - at this point I felt the writing was just plain lazy, basing the show on production design and HBO coolness. The flashback scenes involving young Nucky were really distracting because of the guy's teeth. Gretch Mol in the nut house wasn't bad, but got repetitive.
But there were some fantastic bits - in particular the action sequences have never been done better. And like I said the finale was incredibly moving, where Nucky does a genuinely horrible thing (throughout the run he's been more bad ass than bad, never as evil as people around him i.e. a Hollywood gangster) and is shown to deserve to die and is executed by someone with the right to do so. The writing picks up too with fresh takes on Capone.
So in the end I feel that the series probably should have wrapped up after three, but the last two installments weren't bad and it did have a satisfying conclusion.