And yet the first two were great, and even the Minions movie was fun enough. There was a formula here that clearly worked.
So what do you do to carry things on?
I mean, they've gone to the trouble of giving Gru kids now, he's changed jobs, he's with Lucy - we've watched his life change over two films.
Sadly, here is where they seem to have slightly run out of ideas.
What's funnier than Gru? Why, two Grus.
You can almost hear the high-fives as the creative team come up with this revolutionary idea.
I mean, if a thing is funny then more thing must be funnier, right?
The thing is...
While being the star of the films (in as much as he's always been the narrative focus), and voiced by a genuine star in Steve Carell, Gru isn't the reason why we watch these films.
It's the Minions.
They're the comedy, they're the heart, they're what people want on their backpacks and lunchboxes.
Which isn't to take anything away from Carell's performance - he's fantastic as Gru - it's just he's not the reason we part with our cash.
So two of him seems like an extra coat of paint on an already painted wall.
Yes, it's now got a slightly deeper hue, but it doesn't essentially change or improve anything.
That gripe aside, Despicable Me 3 (or Despicable M3 to give it it's "official" title) isn't terrible.
With former child star Balthazar Brat as the villain, there are a lot of very well-observed 80s gags, both visual and verbal, and the soundtrack is awash with nostalgia.
And there's all the usual high-jinks, chases, gadgets, visual gags, and the Minions doing what the little banana-coloured berks do.
Not enough, to be honest with you, we could have done with more, but they're still there and we still love them.
And Lucy (voiced once more by Kristen Wiig) is again on the money and enjoyable company to be in.
And, as with D2, there's an underlying theme, a weightier message to pick up on if you want (this time the theme is family, and what makes one).
But equally, you can let that pass you by.
And there in lies the real problem with D3.
Once the hilarious opening sequence is over, the rest of the film just kind of happens.
Yes, there are laughs, but they're more chuckles and giggles, perhaps a smirk or two.
The guffaws of yore are a bit thin on the ground.
By the time we're in the final third, it feels like we've been here before.
In fact, you could watch the three trailers and you've pretty much seen the whole film.
All that said, younger fans of our acquaintance have reported back that they loved it - and as it's really for them, who are we to disagree?
But for the grumpy grown-ups who are being dragged along, there's not enough to really keep you entertained for 90 minutes.
But you might find yourself humming a Gilbert and Sullivan classic on the way home.