They took some getting used to at the start, but I wouldn't say they are terrible.
Like you Mop it up, I hadn't really played many racing games outside of Mario Kart for many years (exception; Excite Truck/Bots!) until NSF:MW, especially on the realistic front of things. The last NFS game I owned was on Sega Saturn, just to give you a frame of reference.
In the beginning every single car I found felt slippery and it looked like a drunk was behind the wheel, I couldn't keep the damn cars straight! Eventually I found the Dodge Challenger which handled a little sluggish compared to the other vehicles I had tried, and this helped me get used to the controls. Before I knew it I was winning races left and right. In fact, I beat ALL of the Most Wanted cars with the Dodge Challenger; only realizing later that I'd gotten better at the controls and may of had an easier time using my new favorite, the Audi.
Months later and I'm ranked 2nd among my friends list, which includes many NWR users. I'd love to dethrone Caliban but geez, that dudes a beast!
I say give the game a try when the mood is right and test out the different cars to see which one handles best to you personally, and avoid races all together until you're a little more used to the handling. The game is just fun enough driving around exploring the scenery/locating other cars or evading the police. Once you're used to one car, take on the races and watch how you'll improve with every win. I couldn't drift to save my life when I started, now I'm taking the tightest turns as smooth as eggs.
Also, it might help to think of it this way; stop comparing it to Mario Kart. The sense of speed is much greater and as a more realistic game, it makes sense that over steering left or right at those speeds would lead to problems. Just be glad it isn't so realistic that you flip the car trying some of those turns. If you still don't like it, that's a shame because I would have liked to add you to my friends list for it.