Well... That was rather anti-climatic. ( Spoilers, obviously. )
From what I've read over the web, it seems like everyone - and I mean Everyone - felt that the ending was satisfactory. I was kinda let down.
Although it was just as technically brilliant as the build-up, the whole " It was Collins all along and he knew the hitman from his past... " conclusion just felt underwhelming. It was nice that they played it small, because all the time you were expecting this huge government conspiracy, but they didn't play it close enough.
Anne Collins was sadly wasted in the conclusion. If they wanted to play it small and personal, they should have included her too.
Think about it; she would've known about the hit - and maybe even would've pushed Stephen into it in a Lady Macbethesque twist -. Their objective would've been a clean state - a new beginning for their marriage - which was possible, now with Sonja out of the way. Sonja was also a potential future obstacle on Stephen's past. It is always mentioned that Anne was the driving force behind Stephen's ascension into his current position, so why not just get rid of her?
Also, Anne's relationship with Cal would've been a charade to manipulate him. This tension would've given birth to wonderful scenes. Plus, it would've further solidified her as the calculating and cold person - as opposed to Stephen's hot-headed personality.
The treads of conclusion then would've been unraveled when Stephen learned Sonja was pregnant - an information Anne perhaps knew before they agreed on the hit. Anne's relationship with Cal already troubling him, Stephen would've begun his descend. Yet, at the middle of all this would've been Ann, trying to play Cal and Stephen against each other.
Anne also had a contact with the spin-doctor, so maybe she would've blackmailed him to keep Stephen under wraps. But instead, the spin-doctor would've tried to tell the story in such a way that made Anne the sole responsible person for the hit...
I mean, hell, I'm just rambling here but the original ending just felt cheap. You have all these wonderful wonderful characters - especially Anne - and you leave them out on the cold like that?
Anyway, all this being said I'm still hoping for the speculated second series. The first one was excellent despite the weak conclusion.