Lack of congruency in a car's design. Lack of elegance.
Many cars today have no rhyme are reason about their design. Often there's no language to it, there's just a bunch of shapes here and there that aren't related to each other. Some companies have gotten better about this while some have gotten worse.
I completely agree.
I get angry every time I see an older Mercury Mariner, because for some reason they decided to put vertical slats on the grill, but horizontal slats on the taillights. Why? It makes the back look like a completely different car than the front.
In fact, I find a lot of cars have very poorly designed rear ends. Especially with a lot of modern, everyday cars, the taillights tend to be randomly shaped blobs with no relation to the design of the rest of the car.
There are some cars that I hated at first but have grown to like, cars I feel the need to defend because the designers tried something different, but the public just didn't like it. The Pontiac Aztec, for example, is often cited as one of the ugliest cars ever made. But it's actually a very coherent design. It has the image you'd expect from a car of that name. Unfortunately, I think the car is just too strange looking, too bizarre for most people to accept it. It doesn't look like any other car on the road, so it's like seeing an alien when it drives by. I'm not saying the Aztec didn't have other reasons for people to dislike it, but I don't think the visual design is one of them.
The PT Cruiser is similar. With all these cars going "retro", it's kind of surprising a car shaped like the older classics was so poorly received by car fans. Yes, it did look plasticy and a bit bloated perhaps, but it could have really gone somewhere. Maybe if it had more defined lines around the fenders and just was in general less bland, people could appreciate it for it's classic design.
Now, there are some modern cars that I think are very well designed, and I'm happy to see that a lot of people seem to agree. The Kia Soul, for example, is just great design. The new (new) Volkswagen Beetle really impressed me too, though it's not perfect. I've liked almost all iterations of the new Mustangs. I've been a fan of the modern Volvo brand in general.
Overall, I'd really like to see design turn to the past for inspiration, not just to bring back old models with modern styling, but to create new models based on the design principles of the past, as you said Keef.