A great comedy comes to an end. It's the day of Tanya's wedding to the annoying Clive, which means Simon has to bite the bullet. But Tanya's nerves suggest all hasn't been well, plus Grandpa has a turn. Will the ceremony go ahead? Will there be a second series? We hope so.

It's the day of Tanya's wedding to Clive, but Grandpa has had a turn. And the bride is clearly having doubts. What started off a little unsurely has developed into a corker of series, and it will be a shame to see it go. Unfortunately, this episode (and indeed this whole series) has been a little overshadowed by the passing in July of actor Geoffrey Hutchings, who played Grandpa.

Complicated family relationships can be played for laughs, which brings me to Grandma's House, now approaching the end of a series that has provoked catcalls and bouquets in roughly equal measure. I'm with the bouquet-throwers, and while I'm aware that you'd have to sit through quite a lot of amateur dramatics before encountering an actor quite as wooden as Simon Amstell, I think he gets away with it, which may indeed be part of the conceit.

The rest of the conceit is that Amstell more or less plays himself, a gay, Jewish comedian called Simon who used to host a TV panel show (Never Mind the Buzzcocks in Amstell's case), and whose mother and grandmother (Rebecca Front and Linda Bassett) are desperate for him to get back on the telly being rude. Last night, they were horrified that he could find nothing funny to say about Peaches Geldof or even Peter Andre, and I was with them all the way; no comedian should ever fall so low.

We've become used to the pattern of this sitcom now - a lot of sitting around in a suburban living room and arguing, with our hero, Simon, generally the odd one out. And when it works, it works superbly. The rhythms of the dialogue are beautifully realised. But tonight things kick up a gear. Simon has been on a self-help course that has convinced him he needs to settle old family scores, do some "letting go of the past and healing the moment". The good news is, that makes him much more patient with everyone. The bad news is, he has invited his estranged father round - guest star Allan Corduner. It makes for some brilliantly desperate scenes.

Simon Amstell is like marmite. Some love his acid tongue while others think he's just a bit nasty. But we all laughed at the 'Preston' incident on Buzzcocks - it was hilarious. His self-penned sitcom, Grandma's House, in which he stars as himself, however, isn't. Simon's not a natural actor. He's stilted, awkward and constantly sarcastic. It's like he never left the Buzzcocks set.

"Look at us all cooped up in here," grumbles awful aunt Liz. "Sitting around all day, talking a load of rubbish... If this was on telly, people would switch over." It's a brave sitcom that includes such a cheeky line, but Grandma's House can carry it off, just. Tonight the family watches clips of Simon's precocious stand-up efforts, which are in fact clips from star Simon Amstell's own early shows as a kid, complete with squeaky voice and zany waistcoat - prepare to cringe. But the highlight is Simon's mother (Rebecca Front) trying to bully him into doing an ITV charity balloon trip. "Why can't you go in a balloon for your mother?" she urges. "You'd look lovely in a balloon!"

Simon Amstell, Larry David and the rise of the 'simcom'

From Simon Amstell to Steve Coogan to Trinny and Susannah, today's stars simply play exaggerated versions of themselves. Does it count as acting? Mark Lawson on the 'sim-com'

Simon Amstell's acting ability is so lacking that it seems to have induced the rest of the usually reliable cast - including Rebecca Front, who's so good in The Thick Of It - to try to compensate by ramping up their performances too far. The result is as painful as quasi-fictional Simon's attempt to chat up an actor, who for the purposes of mild farce ended up in the front room with all the over-the-top relatives, matchmaking with glee.

Unlike other bad sitcoms, you can't accuse Grandma's House of being thrown together with too little thought: if anything, its problem is the opposite. On paper, the comic potential of Amstell's embarrassment coming up against his knowing self-awareness is there, but on the screen it comes across as simply annoying on all counts.

I'm enjoying Grandma's House (BBC2) more and more. Simon Amstell can be ever so slightly annoying as himself. But I like the other characters - mum's boyfriend Clive with his crap jokes and his positive-thinking, self-help book attitude; Grandad with his "cancer" (which may be a raisin); Auntie Liz who no one takes any notice of unless it's to have a go at her appearance, especially now she's got her frilly Prince blouse; and young Adam who can't decide whether he's a child or a grown up - he knows he's interested in "pussy" but he also dropped his phone in the loo when he was taking a photo of his poo.

I watched this one twice and enjoyed it just as much second time round; that's a good sign in a sitcom. I don't know how long it will feel fresh. Could it survive a second series? I'm not sure. But right now there's a subtlety and a sharpness about it. And yeah, it's funny.

Have you been watching ... Grandma's House?

Three episodes in and Simon Amstell's sitcom has hit its stride. Is this the best-observed comedy family since Frasier?