It would be a shame if the car's styling was the only aspect people debated though, because its engineering is even more intriguing. It's perhaps one of the most innovative, relevant designs in years, a car that suggests Citroen is at the start of another truly creative streak, such as it enjoyed throughout most of its pre-1990s history.
Car manufacturers have finally begun to realise that reducing weight is a vital part of our motoring future, but weighing in under a tonne, the Cactus makes its C-segment competition seem bloated in the extreme. Yet no fancy carbon fibre structure is employed here, nor even bumper-to-bumper use of aluminium. The latter metal is used in places, but only as part of a cleverly-designed steel chassis that maximises strength where it's needed and minimises it where it isn't.
Weight has been shaved from other places too -- the bonnet is alumnium, rear electric windows are ditched in favour of pop-out units, the rear seat bench is a one-piece folding affair rather than a split bench. This would sound downmarket were it not for clever materials use, giving the Cactus the appeal of an urban loft apartment rather than student digs.
Like BMW's recent i3, Citroen has simplified the dashboard -- buttons are minimised, functions are accessed through a simple display screen and there's another display in front of the driver, replacing the usual instrument binnacle. The passenger-side dash contains an enormous storage cubby, facilitated by moving the airbag into the roof, from where it fires down to protect the passenger. And of course, there are "airbags" on the outside, too -- called Airbumps, they protect your panels from errant doors and shopping trolleys at the local supermarket.
Few of the Cactus's features could really be considered a compromise, yet it gives the car a distinctly different flavour to the homogenised hatchbacks we've unwittingly got used to.
But it makes me think, and will hopefully make other designers think, too: What other new ground can be broken in car design?
There's certainly room for change in the cabin. Dashboards are largely superfluous these days, enormous slush-formed lumps of plastic serving little purpose beyond holding a few bits of wire, a vent or two and on the passenger's side, an airbag.
Citroen has proven that the airbag can live in the roof, so why does the passenger need that lump of plastic at all? That space can be extended outwards for an airy, spacious passenger compartment. Ditto the driver, whose controls and displays could easily be centred around a simplified steering column and dashboard combination. It would make for a less cocooned, hemmed-in feeling behind the wheel, surely a component in the aggressiveness of modern drivers.
Ergonomically-designed, thinner seats could offer all the comfort of today's pews without the need for so much adjustment, and the weight and space they save in the cabin would both be beneficial -- the former for performance, handling and economy, the latter for space and boot volume.
Externally, there needs to be a revolution in materials use. Light weight is clearly the way to go here, but easy and cheap to replace would be appealing too. Provided the car's structure is sound, there's little reason we can't return to simple, bolt-on panels. Make those panels from a light-weight composite too, rather than steel or even alloy -- plant fibres in natural resin would make for an easily-formed, environmentally-conscious, fully-recyclable and lightweight component. No risk of rust either, and it could even spur a new kind of exterior finish, using naturally-coloured fibres to give your car its hue with a clearcoat finish to highlight the texture beneath.
Powerplants? Choice would essentially be free. Electricity increasingly makes sense, but the Citroen Cactus's 91 mpg combined figure is proof the internal combustion engine still has life in it yet. Because the car is light, economy would be better than the alternative whatever engine you use, and performance would prosper too.
I've barely scratched the surface of what's possible if given a free reign with design and construction, though. None of these ideas are even new - but combined, as some are in the C4 Cactus, they could take the humdrum passenger car in an entirely new direction. Given a clean sheet, how would you revolutionise the family hatchback? I'd love to hear your thoughts and ideas below.