I am not sure it was based on a true story: it was based on the non-fiction McMafia by Misha Glenny with particular reference to one on two chapters.
I thought the last episode was very good: Alex I don't think was ever going to turn out a goodie: he was either going to be as he was or dead. The whole series I think was supposed to show him getting sucked in, but actually what I think the last episode showed rather well was how much he was actually really Russian, so maybe it was not so much getting sucked in, as revealing his true self or rather his true "genes".
That wasone thing I loved about it: it showed the cosy British couple gradually torn prised apart as the cool Brit turns out to be not what he seems, while at the same time the foreigners, especially Vadim, Ilya etc are all shown to have a human dimension.
I felt almost sorry for Vadim at the end: when he asks Alex if he supports any particular football team, and Alex says "no" Vadim retorts: "It doesn't surprise me". (Alex develps a sudden affinity for Real Madrid tho when he needs to create a diversion earlier).
It does look set for another series: I think the makers were going to see how popular it was and then decide.