We shouldn't assume that Ricky Gervais spends too much time worrying about bad PR, but his latest outing in Derek - a one-off mockumentary about a care-home worker with learning difficulties - went some way to appease critics of his cheerfully ironic slant on differently abled people. Well, further, shall we say, than his sitcom about dwarves.

Gervais's talent for creating mischief offstage increasingly makes it difficult to view him through fresh eyes when he's on it. But there were no "mong" moments here. And if his chin-thrusting gurn in the role of the slow-moving Derek impressed more as a feat of endurance than dramatic ingenuity over the 35 minutes (the threat of lockjaw surely loomed over this production), that was no reason to doubt his sincerity. Derek bobbed eagerly among the old folk, hogging the roving camera like a child with a favourite uncle to entertain. It didn't take long to see his world of small pleasures and mutual give and take.

It's true that Gervais found room for a little light slapstick - once Derek had contrived to sit in his own rhubarb and custard it was only a matter of time before he toppled into the fishpond - but you didn't get the idea that we were there to poke fun at him. Derek was dim but he was kind and won kindness in return. And there was only one side to be on when he was baited in the pub by "chavs" (as they were described in the credits; Gervais hasn't quite lost his appetite for tweaking the noses of Guardian types), though the tone wobbled into farce when Hannah - manager of the home, and Derek's minder - was required to deliver justice with an unlikely comedy headbutt.

There was a gentle romantic subplot featuring Hannah - a familiar tongue-tied man-yearner in her 30s - and a handsome visitor, while Gervais's pet idiot-philosopher Karl Pilkington (handyman-bus driver Dougie) in a bad wig offered his usual baleful observations. But not much could halt the drift towards sentimentality, which started with Derek going off to buy a lottery ticket for a much-loved frail, elderly resident accompanied by the sort of plaintive piano that could only signal bad news. Derek tugged too importunately at the heartstrings to achieve pathos but I suppose there are worse crimes than trying too hard.

This touching, one-off comedy drama is written and directed by Ricky Gervais, who also takes the lead role as Derek, a vulnerable adult working in an old people's home. You might expect Gervais to run cynical riot in this setting but he's in surprisingly sensitive form. It's down to Karl Pilkington, Gervais's long-suffering puppet in Sky1's An Idiot Abroad, to nab the darkest lines as Derek's best friend and landlord, Dougie.

There's a one-off Ricky Gervais comedy-drama on Channel 4 tonight called Derek (10pm).

It's a bit of a departure from Gervais' normal stuff, the main character being a simple but honest guy who works in an old people's home (alongside his pal Dougie, played by Karl Pilkington, who I have to say doesn't seem to be acting much).

It's hard to imagine this one would have got commissioned without the involvement of Ricky Gervais.

He writes, directs and stars in this one-off comedy drama about a simple soul called Derek who works in an old people's home.

His mate Karl Pilkington is in it too (as Dougie), in what is easily the worst hairpiece in TV history.

There are occasional smiles, but this doesn't have the savagery of Getting On, the BBC comedy on how we treat the elderly.

This is a much more sincere, poignant little piece and although Derek and his co-worker Hannah (Kerry Godliman) love their jobs, the fact remains that most people have a horror of ending up in a place like this - even if it is only on the telly.

Ricky Gervais follows up Life's Too Short with a show about a simple, vulnerable man working in an old people's home. Brave, but this isn't the moment where Gervais is consumed by political incorrectness once and for all: Derek is nearly a brilliant reinvention.

You'd have to try hard to read Gervais's portrayal of slow, sweet Derek as mockery, and the sad ending is up there with David Brent's "Don't make me redundant" meltdown. Kerry Godliman shines in a supporting role as Hannah, the care worker who is Derek's best friend and is thwarted, selfless, burningly sad but endlessly compassionate - every moment she is on screen is sigh-inducing magic.

But Derek falters because Gervais, who writes and directs without Stephen Merchant, is too reliant on tropes from his previous work. The action is shot as a documentary about the characters, a device that doesn't add much and highlights the occasional, inappropriate similarity between Derek and Gervais's other creations. Casting Karl Pilkington as another of Derek's colleagues also breaks the spell, and sometimes the mix of slapstick and sensitive drama is uncomfortable.

Despite some brilliant cameos from Liam Neeson and Johnny Depp, we're thrilled to see Ricky Gervais leave Life's Too Short behind and return to the workplace sitcom. Gervais' new Channel 4 special is set in a retirement home and features the acting debut of An Idiot Abroad presenter Karl Pilkington as Dougie the caretaker. While some (particularly fellow comic Stewart Lee in the Guardian) have pre-emptively damned Derek as insulting, others are praising the script and calling for a full series - all we know is that we can guarantee #derek will be trending on twitter tonight...

Derek represents something of a trap for critics hoping to hammer home the idea of Ricky Gervais-as-heartless-bastard. Carrying out an unspecified role in a provincial care home, Derek's an eccentric. Indeed, with his permanent gurn, inadvertent gift for physical mishap and general air of bewilderment, some might assume that he's in some way disabled and draw the obvious conclusions about his creator's motives. Gervais says not. Instead, Derek is marginal. He bonds with the old folk, indulges in nonsensical conversations with caretaker Dougie (a debut role for Karl Pilkington) and imagines himself as a possible suitor to the home's manager Hannah, who, while lonely and unfulfilled, is way out of his league.

Derek is hard to judge on the basis of a pilot. Some of the comedy is incredibly broad. Derek sits on a pie. Derek falls in a pond. We're laughing at him, but, before long, we're sympathising too. A couple of scenes hint at the show's potential tenderness and tragedy and suggest that a series - which Gervais is already writing, without frequent partner Stephen Merchant - would be worthwhile.

So I suppose we'd better get Derek (Channel 4), Ricky Gervais's little (comedy?) drama set in an old peeps' home, out of the way first. To begin with, I can't see what all the fuss is about. OK, so the title character isn't the sharpest tool in the shed, but is that really mocking disabled and mentally ill people? Can you ban simpletons, even ones who are bathed in a warm light? Baldrick, Bean, Bottom, all cancelled, by PC plod?

I think the columnists and critics who have been sharpening their pencils to stick into Ricky's eyes are doing so because of previous lapses in judgment. I mean Mong-gate of course. But Derek isn't controversial.

Trouble is, nor is it very good. The whole mockumentary thing feels tired now (and what are these films being made, do you ever wonder that?). There's a lack of confidence about it too. The humour (if you can call it that) yo-yos between standard been-there Gervais Office squirmy awkwardness and sit-in-a-custard-pie/fall-in-the-pond slapstick.

Most of all, though, I'm not feeling the character - I'm neither moved nor amused by him. In The Office and Extras, Gervais was basically playing himself. He was someone you could loathe and love at the same time; you could begin to understand how it would feel to be him. Derek, a much more sympathetic character, is someone else, and so requires more acting. Which, perhaps, given this awkward show of haminess, isn't his forte. Neither is it Karl Pilkington's, as Derek's sort-of mate - not much hope of best supporting Bafta, I'd say, though he's probably straying less far from his real self.

Its a shame. I really wanted it to be good. To shut up the Gervais bashers, for one, who may even be more annoying than Gervais himself. But also - and mainly - because he used to be so good. Remember?

This is a Ricky Gervais programme for people who don't like Ricky Gervais. Derek Noakes (played by Gervais) is a retirement home worker with learning disabilities. He sports greasy hair and bad cardigans, but he always puts others first and is kind to the old people he looks after. He also loves Rolf Harris and Deal or No Deal.

So far so predictable: Gervais has seemingly picked another vulnerable target to poke fun at, while no doubt purporting to break down taboos. But remarkably this is not the case. Gervais is not making fun of Derek, or anyone, it seems - he's celebrating him, and the other outsiders who work in the home (including Karl Pilkington in his debut acting role as Dougie the caretaker, and Kerry Godliman who plays Derek's best friend Hannah). It's a genuinely fond and amusing script. When one of the old people at the home dies, Derek remembers the lady once telling him: "It's more important to be kind than clever or good-looking." "I'm not clever or good-looking... but I am kind," Derek says, holding back the tears. Gervais is apparently hoping this pilot episode will be commissioned for a full series but Channel 4 has billed it as a one-off comedy drama. They'd be fools to let it go.

Once Ricky Gervais gets hold of a good idea he really doesn't like to let it go. Employing his trademark mock-documentary format yet again, Derek follows its socially awkward, visually unprepossessing middle-aged hero as he shambles around his workplace, a care home for the elderly.

Although the show is resolutely ambiguous around whether Derek has learning disabilities or not, Gervais' performance in the title role is both sensitive and sympathetic. Disability rights campaigners can rest easy, if this pilot episode is anything to go by.

If the show's framework is disappointingly unoriginal, the tone is a radical departure from anything Gervais has done before. The Office, Extras and Life's Too Short all had their moments of poignancy, but Derek cranks the pathos up to full throttle and the result is bitter-sweet and disarmingly affecting. Between Derek being ridiculed, confounded and bereaved there isn't a lot of room left for comedy, and viewers tuning in for a laugh riot will be disappointed.

But there is still a wealth of comic detail to enjoy, particularly around Derek's friendships and relationships. Karl Pilkington, formerly Gervais' stooge but here making his acting debut as co-star, delivers a particularly delicious deadpan turn as best mate Dougie.