Good: great looking, great cabin, good to drive, exceptional refinement, practical.

Not so good: back seats could be a little roomier, cabin could be more inventively styled.

None of us are truly objective, no matter how hard we may try. Journalists, at their best, are supposed to aspire to Mr Spock levels of Vulcanic detachment and logic. We are supposed to be mere observers, standing at one remove from that which we observe, and beholden to naught other than hard, solid, fact.

What rubbish. No one can actually do that. Strain every intellectual sinew that you possess and you might achieve a tenth, a twentieth of that ideal, but your own deeply-held instincts, tastes, desires and, yes, prejudices, will count against your effort. When it comes to reviewing consumer items (and cars are ultimately just that) it goes double - we feel things about cars, we become excited about them, passionate about them. I'm sure that there are enthusiasts of fridges and steam irons out there (Rule 34 and all that...) but when it comes to cars, they are almost uniquely imbued with our enthusiasm, in a way that no other purchasable collection of metal, plastic and rubber is.

The converse is also true. Enthusiasm has a flip-side, a yin to its yang and that is when you drive a new car on a day when you're just not into it. When you've gotten up on the wrong side of the bed, so to speak. When all the post is bills, when the TV's on the blink, the coffee is cold and the cat's done a poo in your porridge. Metaphorically. Possibly literally.

It must have been just such a day when I first drove the new Audi A4, late last year, as I simply couldn't get on with it. Technically astute and mechanically polished it may have been, but I just didn't connect with it and wrote it off as a mildly dull photocopy of the previous model.

I should not have been so hasty. Nor so grumpy. Nor so dismissive. Fast forward to this week, and another A4 sits on my driveway and this time the enthusiasm is positively rampant. Perhaps it's to do with the colour - the previous A4 I drove was a dull, plain silver, but this one is a bright, strident red. Perhaps it is because it is the Avant estate model, as I do love a good estate.

For whatever reason though, suddenly the A4 has snapped into focus for me, and comes close now to unseating my current favourite car in this segment, the Mercedes-Benz C-Class.

Let's go step by step. First off, the engine. The 2.0-litre TDI with 150hp and 320Nm of torque is the most basic engine you can actually get in an A4, in diesel terms anyway. You would assume that means it is slow and sluggish, and a little noisy. Not so. Decisively not so. In fact, I'd say that this engine now takes the cake, biscuit and scone as the most refined four-cylinder diesel engine on the market. It is astonishingly quiet and un-diesel-y, to the point where, over several days' driving, I think I heard it clatter just the once. It has plenty of performance too, with a solid stream of middling-revs torque that makes progress truly effortless, and which is well combined with the seven-speed S-Tronic dual-clutch automatic gearbox. This transmission has been feeling its age a bit lately, and has in some cases been overtaken in smoothness by Mercedes' 9G-Tronic, but here in the A4 it feels just about right again, rarely if ever misjudging a ratio and making its manual-shift mode more or less redundant. Which is as it should be with a good automatic.

Then there's the dynamic setup. Yes, those of us of an enthusiastic bent assume that Audi will always stick to its satirical acronym of Always Underwhelming Driving Impressions, and indeed the A4 does have that built-in sense of weight and heft that Audi engineers have previously told me its customers desire. Yet it's a veil - beneath it is a sense of lightness and agility quite alien to most previous front-wheel drive Audis. True, a BMW 3 Series or Mercedes C-Class (or a Jaguar XE or Lexus IS for that matter) will out-handle and out-entertain an A4 with their delicately balanced rear-drive layouts, but within the limitations of its setup, the A4 is little short of excellent. Even the steering feels good.

As does the ride quality. Previously, selecting the S line package for an A4 (or pretty much any Audi) was to essentially get on to first name terms with your local chiropractor, but here is evidence that Audi has learned BMW's trick of getting its M Sport equipped cars to be comfortable. Even with the lower and stiffer springs it is genuinely very good. Aside from a slight sense of too much stiffness over poor urban surfaces, there is only well-damped precision here, and no harshness. It is commendable.

Finally, there's the interior and here, oddly, I think that it might actually be the A4's weakest hand. Audi has for ages been the king of cabin quality and layout, but now I think that crown has passed to Mercedes (and Lexus has more interesting ideas than either). There is nothing to fault inside the A4 in terms of design or quality, but it really needs the optional 'Virtual Cockpit' digital instruments to enliven proceedings, and the fact that the central infotainment display isn't actually a touch-screen is a source of constant annoyance. There is also a slight lack of legroom in the back seat, which is a shame for a car that will be chosen as a family appliance by more well-heeled parents.

At least the boot is good - 505 litres of luggage space is more than useful (albeit far less than that of in-house-kinda-rival the Skoda Superb Combi), and the way the tonneau cover whirrs electrically up and down as you open or close the tailgate is far more useful than any electric boot lid.

Perhaps it was down to my mood. Perhaps it was that the weather is sunny, the school run still a few weeks away, or maybe I simply clambered out of bed on the correct side. But suddenly the Audi A4 makes sense to me. More than that, it has become desirable.