Last night's viewing: Love/Hate, Channel 5 Who Do You Think You Are?, BBC 1

You know you're obsessed with a programme when you can't stop cornering unsuspecting friends and asking if they've discovered it yet, only to sadly shake your head when they say no. Such was my problem with Love/Hate, Channel 5's addictive Irish crime import, which concluded its all-too-brief first season last night.

On the surface, this tale of Dublin hood rat Darren Treacy (a compelling Robert Sheehan, his eyes constantly making promises his mouth couldn't keep) was yet another attempt to take The Wire's panoramic vision of gang life and death and translate it for an audience closer to home. However, this was more than a mere Wire wannabe, offering something distinct and compelling in its own right.

All the expected ingredients were present: the businessman gangster (Aidan Gillen at his smirking best), his unhinged brother, the conflicts between family life and gang "work", the double crosses and betrayals, the sense that our heroes are merely foot soldiers in a wider war.

There were hints, too, of Trainspotting: not since Danny Boyle's 1996 film has a drama been so in love with a slow-motion tracking shot followed by some speeded-up footage set to a banging soundtrack.

Add to that a strong ensemble cast, an intelligent script and a superbly tense denouement and you have a sharp albeit relatively straightforward gangland tale. What pulled Love/Hate out of the ordinary was its treatment of religion.

This was a show marinated in Catholicism. It was present when the talk turned to purgatory and in a discussion about a dead baby's soul. And it hovered unspoken in the scenes of candles in churches, the talk of confession and the conversations with the dead at freshly dug graves.

Most of all, it was there when Darren answered gang boss John Boy's bald statement: "Who are you to judge? Only God can judge" with the equally bald: "I don't believe in God." In one simple, bleak and brilliant moment, the conflict between the old Ireland of God and ghosts, and the less spiritually beholden country pushing up through those ancient roots, was laid bare.

Darren's refusal to acknowledge God would be commonplace in a drama from the UK. In an Irish series it stood apart, asking difficult questions of both its characters and the audience at home. If you've yet to see it, track it down quickly before the reputedly even stronger second season arrives on Channel 5.

Difficult questions were also being asked on this week's Who Do You Think You Are? The long-running BBC series has felt stale for some time but occasionally they pull out an episode with the emotional force of the early days – it happened recently with Minnie Driver and again last night with Lesley Sharp. Sharp, adopted at six weeks old, never knew her biological father although she tracked down her mother, Elsie, in 1990.

The subsequent story turned out to be one of those quietly heartbreaking tales of ordinary families and the secrets they hide. We learnt that Sharp's father, a married man of two, never told anyone of this other child's birth – "I don't know why he didn't just mention it to me when we were having a drink together," said her older brother in stoic disbelief – before learning too of a very different man, Sharp's great-great-grandfather, whose definition of family didn't stop with recognised blood kin.

In the end, an emotional Sharp's thoughts turned not to the man who broke her biological mother's heart but to the one she grew up with and called Dad. "Who you're adopted by can have a profound effect on your life, I got very lucky," she said. And, just as in the glory days of season one, it was hard not to cry.