First there was Jane Fonda in Monster-in-Law, then Diane Keaton in Because I Said So, and now we have Smother -- which is about another mother from hell, also starring Diane Keaton.

Marilyn Cooper is the manic matriarch, who, convinced her husband is having an affair, lands on the doorstep of their son Noah. But Noah's already got problems. He's just been sacked from his therapy job. His wife Clare's pressuring him to impregnate her and her nerdy cousin's crashing on the couch.

What Noah really doesn't need is for mum to move in – and stay indefinitely. Of course, that's just what she does.

At first, Smother is an uphill battle because the script and performances are rather broad. Dax Shepherd is so droll and downbeat he makes Ray Romano look like Fred Astaire. And as the frazzled flake Marilyn, Diane Keaton seems like a cartoon version of a freaky mum. Added to this, Liv Tyler's very wet and schmaltzy as Clare.

Surprisingly though, once we're in the rhythm, Smother gains momentum and becomes pretty funny.

Shepherd's comedy is an acquired taste but his deadpan sarkiness earns some big laughs. And while he and Tyler have no chemistry as a couple, that actually makes their fights believable.

Likewise, Keaton eventually adds enough facets to Marilyn to make her credible and amusing. There's also great work from Mike White as Myron, the loafing screenwriter cousin.

Realising we won't buy in anyway, Smother doesn't tug the heartstrings too hard so we're spared saccharine sentimentality. Instead, we can just enjoy Shepherd's jokes about tiny underpants, Keaton playing spy and Mike White pitching his dream screenplay – about a half-man, half-mosquito superhero fighting in the Vietnam War.

Now, that's a movie I want to see.

I'm not sure if this one's for the whole family, given the arguments it might provoke, but as harmless fun it rates three stars.