Comedy Lab, Channel 4

Comedy is difficult to get right – for every Outnumbered, fizzing with smart dialogue and natural performances, there is a Big Top (the circus-based show so risibly bad it was offensive).

Complicating matters, there is undoubtedly an audience for innocuous pap such as My Family – going for a decade now – making it acceptable to schedule such middle-of-the-road fare as Life of Riley, the defiantly mediocre Caroline Quentin sitcom that reached its conclusion on Wednesday.

So the seven experimental one-off shows broadcast last week as part of Channel 4's Comedy Lab strand had quite a balance to strike – between being innovative enough to convince the commissioners to give them a full season, and sensitive enough to forge as broad an appeal as possible.

Ever since its inception in 1998, the quality of Comedy Lab's output has been as irregular as the intervals between its airings. Notable alumni include Ricky Gervais and Peter Kay; less happily, it has also hosted some stinkers that have sunk without trace. So, to which end of the spectrum would its latest collection tend?

The first programme up for inspection was iCandy, a showcase for Irish impressionist Liam Hourican. There was good: Hourican's mimicry of Louis Theroux, interviewing Hitler in his bunker ("I'd never met the most hated man in history before, but I hoped we'd get along") and Peter Stringfellow – a spot-on vocal imitation as the legendary lothario teaching young hoodies a thing or two ("I give them a steak and a dance, and they turn into gentlemen"). There was bad: a TV life coach who used to be a mobster. And then there was ugly: the Mancunian driving instructor whose moods swing faster than you can hit the dashboard. Hourican has talent – but he needs help with the writing.

Airing directly after was the sketch show Happy Finish. A Ghost Whisperer pastiche hit the mark ("Get her to ask me a question only I'd know the answer to." "Where did we have our first kiss?" [Long pause] "Get her to ask me another one"), while a skit about the quotidian vapidity of time travel played impishly with expectations. But the high point was the introduction of the Department of Internet Hate – an underground government arm that writes those ferociously derisive comments that appear under YouTube videos, with invective just short of Malcolm Tucker's finest. Only an odd piece about the fatal consequences of illegal downloading really failed – puerile and not nearly as clever as it thought.

The same cannot be said of Penelope Princess of Pets. Written by and starring Kristen Schaal from Flight of the Conchords. It did not try to be too clever, just surreal. Penelope has 3,769 hours to save the world by killing Thomas Stone MP (Julian Mighty Boosh Barrett), and stopping his fiendish plot to start a war between humans and animals. With crackerjack repartee ("Is she dead?" "Not technically." "Figuratively?" "No, but Sam says she is to him") and a delightfully silly sensibility, this is a show with legs.

Far less likely to get an extended run is The Secret Census, in which comedian Jack Whitehall asks: how honest is Britain? For example: would people lie in court to save ex-Hollyoaker Gemma Atkinson? (Not surprisingly, more men than women would.) The only twist was that none of those taking part in the "poll" knew they were taking part. As a barometer of the state of the nation, it's pretty simple stuff, and Whitehall can do better than this.

Next up was Filth, a sitcom set around a lads' mag. Filled with clueless idiots who don't exist in real life and a nastily juvenile approach to sexual politics, it made Two Pints ... seem like The Likely Lads. When Danny Dyer is the best thing in a show, you know it's time to move on.

MovieMash, a spoof film-review show co-written by Dan Renton Skinner (Angelos Epithemiou from Shooting Stars), had some merit. Its twisting of celebrity interviews (the best being with Steven Seagal – largely because he gives such odd answers anyway) was passable, but it was its short features that stood out, most notably a motion-capture filming of Vera Drake.

Finally, Hung Out desperately wanted to be Peep Show, but lacked its quality. A house-share sitcom, its dialogue was realistic – but so much so that it wasn't always terribly funny.

Just as some of these shows will fail, it will be the successes that we will remember. And the ultimate congratulations must really go to Channel 4, for continuing to devote airtime and resources to a project that will keep the country chuckling.