The game is great until you are trying to make something look as good as it performs. Performance is easier to master than looks. Planes often look choppy or are extremely heavy. Even with mods it is still extremely tedious to make a small area look good. There are a few mods that allow you to nudge parts into place and to shape or rotate them. If this could be added it would be great.

-tires could adjust give in the settings
-car engines could be tuned for torque AND horsepower. I don't want a 60,000Lb semi truck going 250mph. It just doesn't work
-ability to rotate parts. Parts at 45 degree angles would help immensly