Episodes, BBC2, Monday<br/>Zen, BBC1, Sunday<br/>Human Planet, BBC1, Thursday

Any new sitcom ought to be allowed a few weeks' grace before judgement is passed.

Miranda managed to short-circuit this process: within about three scenes of episode one, I'd say, you knew whether this was appointment TV or a very good reason to tackle the tax return.

Episodes, by contrast, tries your patience before you've even caught a glimpse of it. That title, its fiddly gestation (it's a British-American co-production being transmitted more or less simultaneously here and there), the rather insidery premise of its plot (British husband-and-wife television writers are invited to Los Angeles to remake their hit show for an American network). And even though it also stars Matt LeBlanc, still best known as Joey from Friends, he's playing "himself". It doesn't exactly put you at your ease, does it?

Nor did the first episode. Having scooped up yet another fistful of Baftas for their show "Lyman's Boys", Sean and Beverly (Stephen Mangan and Tamsin Greig) succumb to a lovebombing from Merc, an American TV network chief: "I wanna have sex with your show!" But their Los Angeles fantasy swiftly proves just that: the house they're being put up in is a leftover location from a tacky reality show, and, naturally, Merc wants not so much to make love to "Lyman's Boys" as screw it and not return its calls. Cue Sean and Beverly's horror as Merc's lackeys painfully spell out the creeping makeover that awaits their baby.

The best moment came with Richard Griffiths' turn as Julian Bullard, the star of the British series, when his audition for the American version shrivels in front of the network execs' incomprehension of his RSC vowels: "He's too ... butlery." Enter LeBlanc (who appeared all too briefly in this first episode).

It was about here, though, that I realised that Episodes' writers David Crane and Jeffrey Klarik might be keeping their powder dry. Call me slow, but here's my best guess: Beverly and Sean aren't merely there on our behalf to point out the clodding philistinism of American network television. No, they're just as mired in their own cultural prejudices – were they really so vain as to offer Julian the role in the American production without their new boss's say so? Do they really think a couple of Baftas entitles them to get shirty with the attendant dolefully manning the entrance to their new gated residence?

Still, though, a long way from hilarious. Apparently, Mangan himself tweeted on Tuesday after the first episode: "Those who weren't wowed, I'd urge you to stick with it. It gets better and it gets better." If you say so, Stephen.

At least the cast of Episodes is speaking the same language, more or less. The BBC's Sunday-night detective drama Zen hops about between English and Italian, and all points between as it careers around Rome. Last Sunday's instalment dealt with the suspicious death of a scion of an aristocratic Roman family – was it suicide or the workings of a mysterious criminal network, the Cabal?

But never mind all that. How weird is it when Rufus Sewell's Zen (a Venetian, remember) shouts in broad English at a few bystanders chatting in Italian? And how come the male leads are British and the female leads are Italians speaking in conspicuously accented English? Actually, I think I know that one: Zen's mother and the secretary are hot stuff. He's living with the former and having an affair with the latter, a heady Oedipal mix to which the sexy accents can only give a bit of oomph. (As for the Cabal, are they the band who give the series its hilariously inappropriate jazz-funk incidental music? If only.)

Human Planet marries the BBC's typically eye-popping natural-history film-making with stories of how humankind has adapted to its surroundings. The oceans were the subject of last week's first episode. The gravelly John Hurt narration, the supercharged theme music, majestic wave after majestic wave...Did I just watch an hour-long Guinness advert?