Petrolheads all over must have been asked this question at some point. Because people assume you know a lot about cars they ask for your infinite knowledge, your philosophical view of what car they should buy. Yet mostly they don't get an answer more extensive than 'Buy Japanese' or something in that direction. This is because a good car can't be defined in a short answer, or at least before the other gets lost in a maze of DSG-gearboxes and multi-link suspensions. But I am determined to give an answer to this life-determining question, at least what I would define as a good car. Feel free to contribute, I am up for constructive criticism.
First and most importantly, you should feel at home in your car. When you buy a car, you shouldn't be annoyed by a badly positioned switch, or that the car responds slower than you want it to. If Barney Stinson were a car journalist, he'd say it has to fit you like a suit. Also, do you actually like it? The car doesn't actually have to be a head-turner, neither should you be slightly ashamed of the badge on the front. If you don't feel like the car represents you or presents you well, turn it down.
Second, your wants and needs. Hatchbacks might in theory fit five people, but practice tells a different story (own experience kicks in here). Don't expect your three lovely kids to fit in anymore as soon as they hit puberty. The middle seat in the back makes a hatchback more of a 4+1 than a five seater. Estates are not only invented to fit a labrador, but the larger exterior gives more space to those inside without necessarily letting down in looks.
Third, the ride. No, you can't expect a Golf Diesel to fly round the Nürburgring in 8. something minutes, or to take a twisty uphill road like Sebastien Loeb does. Though it should be satisfying and solid during normal use (and a bit beyond that). Part of this will be affected by the tyres supplied by your dealership, the standard Ecotyres you get with a Prius will make you save a glass full of petrol every 1000km, as well as send you into a tree when you encounter some slippery conditions.
Fourth (still important), reliability and build quality. Sure, your Citroën DS3 may have stunning looks, but how do you look when you've got to pay the bills? Factory guarantee might not be interesting when you buy a new microwave, but in cars a seven year guarantee on your Kia might eventually pay off. One other note is that brand new models will have some bugs that take one or two years to be filtered out (hence the facelifts of models).
Fifth, clever engineering. This might be a personal judgement by me as I love things that are developed well and thoughtfully, but I think everybody agrees to some extent on this one. Surely, nobody will be impressed by the lower suspension and closed grille on the Bluemotion/Ecoboost/DrivE like models, but those things work without any serious drawbacks. Or seats that fold without having to pull your wrist out, all this shows that a car has been thought true by the right people, lovely.
Sixth, the balance between eco and driving, it's a thin line between saving fuel and sportivity. Take in account that the majority of the time you'll be doing trips which don't require a rumbling V8, yet to much eco stuff on your car can ruin things. An example of this is Electrc Power Steering, it saves you 0.2 liter every 100 kilometres, and also prevents you from any accurate steering input.
At the bottom of the list we find the extras you get in a car, God forbid you don't choose a car on the base of its extras. A rubbish stereo might be a valid argument to turn down a car, but don't judge a car for the fact it has only 8 speakers instead of 12. Seats with built-in vibrators and carpets made from Brazilian badger fur are not only useless features but also horrible subjects at dinner parties.
