You know what I was thinking? In the titles, the Dean should have been a different kind of animal – a cat, say – rather than a human.

This is where I am with Lab Rats now – I’m feeling all-series reflective. I’ve become inured to the messy editing, the sound, the flood lighting, the clunky digital effects. Now it’s mostly about the bigger picture. A Diary may have featured the unwelcome return of the animated transitions, but it also made good on some great big laughs. Coupled with the uneven rhythms, it’s a typical episode of Lab Rats.

Though, if I’m being honest, A Diary is probably my favourite of the episodes I’ve reviewed. (John, that lucky bastard, got to revel in A Seven-Nighter and for that I will always hate him.)

Some specific good stuff this week to start with, then. Dr Beenyman’s dad, chatting to his son in the lab, ends the conversation with “Should I put your mother on before I go?” Which is almost as perfect as a joke can be. It’s a feed line and a punch line in one – it tells you this is dad-ness at its most generic, then gets a laugh out of it.

Even better is the father’s – apparently habitual – offer of a pound, to which Beenyman replies “If I had a –” And he stops. Because we’re already there. It’s a deconstructionist joke, crediting the audience to know exactly where it’s going.

If the series had kept up this kind of pace in the dialogue throughout (hard to achieve in a commercial half-hour, mind you, let alone a BBC one), Lab Rats would have been a no-brain winner. The trouble – and this goes for all six episodes – is that for every pair of pitch-perfect gags like the two above, you get one that doesn’t realise it’s far too predictable and carries on anyway, then one that’s ruined by bad timing.

So when we get the dad’s “Commemorate November 5th” ramble, we’re so far ahead of the joke – that he’ll be celebrating the date with fireworks and a burnt effigy – that we just had to wait. You sit it out.

Then “You’re wearing two pairs of dungarees” – should have been a decent giggle, but once again the timing of the line to the visual was crucial…and missed.

In the struggle to fill the space with a high joke-rate, Lab Rats finds itself forced to scrape the barrel occasionally. “Oh no, has X been doing Y again?” has become a stock filler that, at this point, you could write for yourself at home; and there always seems to be a character tangentially dipping into a mostly-unrelated anecdote with the standard “I Xed a Y once” bridge. The obvious, standard jokes need either dropping, or deconstructing.

The usual flaws, then, but when the jokes hit right, they really do hit – and in this episode especially. “You can’t tell a book’s ruined by its cover” is lovely writing, as is the constant repetition of the term “rape ink”. The melted Lionel Richie Blu-Tack sculpture was fab (and just reinforces how much more appropriate physical props are than digital tricks). And Beenyman’s discussion about the thermostat turning into a weatherman parody was spot on, and was rendered absolutely legendary by the perfectly timed cut to Cara as ad hoc ‘newsreader’. Flawless.

On the other end of the scale we have papier mache dungarees – a nonsensical moment that achieved nothing (and could have done, if only it had been set up earlier that the machine had such a bizarre effect on its contents…or if there had been a subsequently-revealed warning sign on the side). Meanwhile the heat-haze effects in the Dean’s office sold things pretty well. So maybe I was a bit rash on that whole physical/digital thing.

The digital pigeon approach was crap, though. (And not really needed – the big laughs came from the reaction, and from the sudden reveal of a blood-and-feathers-covered set.)

So what’s causing this hit-and-miss problem? Glad you asked – clearly you’ve noted my interesting CV and want to learn more. Thanks for calling.

The first thing is plot. There ain’t enough of it. With almost 29 minutes to fill, too many of the stories have been short on turns. As with A Bee, where the rivalry element should have had double the back-and-forth we got, A Diary needed to reach further with its various strands.

This is the main story in summary: Alex’s dad shows up with what may be Scott’s diary to authenticate it. They do so by looking at it. The diary is accidentally damaged, and is taken apart to be dried, then is further ruined in the ‘spinning machine’ in an attempt to dry the pages.

It doesn’t twist. That’s the problem. What you have there is the first half of a story – ruining the diary and then admitting it isn’t a full tale. Father Ted would have used this up before the ad break. The Simpsons would have blown through it in their first three minutes. Not that speed is everything, but ‘ruining the important object’ is a standard sitcom plot – the second half is ‘frantic and increasingly lame attempts to hide the problem’. Which, a few lip-service lines aside, we didn’t really get. We have the inception, but we’re lacking the escalation. (Yet another reason why only a couple of episodes have truly earned the “Oh f-“ ending.)

If the jokes were all hitting, plotlessness wouldn’t be worth mentioning. But these guys are at their best when there’s something bizarre to react to, when they have more weird toys to play with, more oddness to encounter. Not ‘big silly’, necessarily – the show’s best moments have often been always-on-light-bulb-type gags – just enough to open new cupboards and to dig through other pockets.

That’s problem number one. Problem number two is this: Who the hell is Dr Alex Beenyman?

I know he’s the guy with the curly hair. I know he’s the one who stands next to the others and explains things. I know he’s intended to be our leading man. But I’m damned if I could describe his character.

The lead in these things is always a rough gig. Nobody’s favourite character in Buffy is Buffy. The funniest person in Cheers wasn’t Sam. Having to carry the weight off the show often means having to be a more simple, direct kind of character. But the good ones – your Frasiers, your George Dents – still have something about them.

So – Dr Beenyman. He’s not pining to get away, or just a little selfish and devious, like Father Ted. He’s not a miserable, angry bastard like Bernard Black. He’s not socially awkward and mistrusting like Roy (from The IT Crowd, do keep up). Does he like where he works? Does he have strong feelings about his situation, or about his colleagues? Beyond ‘mild exasperation’ does he feel much of anything at all?

His dad being so utterly generic fed into some lovely jokes, but there was a price: it continued to leave Alex with only a single dimension. His character description could already be summarised in a short paragraph, now it seems his childhood could be covered in a single line: ‘more or less like every other middle class boy’s’.

Arguably, there’s an episode in this. Alex realising he has no character traits whatsoever. Maybe he donated them to medical science. Maybe they need to inject some new ones. Hell, right now I’d settle for the show playing more heavily on the tall/short visual he has with Cara...

Two points. Fundamental, but solvable – just like the production quality issues. Fix these and Lab Rats 2.0 could be doing great things. These two points are, for me, the major causes of the hit-and-miss.

Sorry, I was meant to be doing a proper review here, wasn’t I? Carrying on.

A Diary proved to be a decent episode for the underused Brian. His encounter with Metal Vicky, the lab’s temperamental thermostat, put him where we needed him – reduced from his cocky status to feigning intercourse with a machine. (The mistake, once again, came from the old and generic execution – in this case getting caught by Professor Mycroft who says, wait for it, “What on Earth are you doing?” Erm, he’s treating the machine in exactly the way you advised previously. Having the perv-in-residence walk in was the perfect opportunity to undercut expectations…and it didn’t happen.)

A key part of Brian’s place in Lab Rats has been his crush on the Dean. Or, at least, it should have been. The hints started well this week, but were quickly thrown away – a missed opportunity when he’s then given a machine onto which to throw himself. Character motivation is key to situation comedy – it’s where everything comes from, whether you’re going for farce, snappy dialogue or slapstick – so wouldn’t it have been wise to connect Brian’s romantic frustrations to his subsequent actions?

Join the dots, guys.

So, okay, Brian and Mycroft don’t make for a great double act. So the studio audience totally missed the neat visual joke of Mycroft picking which set of peanuts to pull from a pigeon-themed board. Hey, it’s easy to complain – and potentially useful if the show goes to a second series (here’s hoping) – but A Diary had loads of Cara, which always makes me happy; it had two delightfully bizarre sequences in the Dean’s office, which again were bound to win me over; it had a smart punchline to the ‘pigeons versus e-mail’ debate; and it did show Alex stepping out into a blizzard pronouncing that he may be some time…which was seeded spot-on with the previous weather gags.

Not as good as A Seven-Nighter, maybe. But these are three totally-deserved stars. A Diary should, arguably, have gone out much earlier in the series run…but it’s a positive note to end on.