Maxi, I really like the look of the rust on the roof of that car. The sides look like you're trying to imitate a car that has had some of the wood siding replaced. That a good idea but the old wood looks more burned than weathered. Try to go a little lighter so you still see the old paint underneath the weathering.
Smoke, it's hard to tell on an oxide red car with no decals but the rust streaks look about the right length and intensity.
Bradley, those MKT units look fabulous! Did you do those yourself? That's one tough paint scheme to reproduce and you don't often see them modeled. Lets see, a 56 car coal train. My passing sidings can handle 12 and 9 cars each. I'd say trying to put me in the hole on my layout (assuming I could even run a 56 car train) would be a big mistake.
Jerome, I don't know Bob and it may be that the camera is showing the car different than it looks in real life but my first impression is that's way too much rust in the wrong places. For example, rib sides rarely have the ribs as the most heavily rusted part of the car since rain and wind tend to keep the faces of the ribs cleaner than the rest of the car. The rust tends to accumulate in the areas next to the ribs where the water and contaminants collect and the rust starts. Check out this picture of an SP airslide hopper as a perfect example of what I'm talking about:
You can see the top surfaces of the ribs remain quite clean while the flat surfaces between the ribs are where the rust and dirt collect. The rust also tends to be much thinner and rarely covers much of the painted on lettering. If it does, the railroad will usually do a patch paint job over the rust and re-stencil the data. Roofs also tend to get much less rusty then the car sides (assuming they are painted roofs like on this airslide) and the hatch areas in particularly don't accumulate much rust because it makes them too hard to open and close. This is one of those areas that shop crews will keep after even if the rest of the roof looks bad because customers complain.
I don't mean to sound overly critical of your work. The rust spotting and streaking really came out quite well. I know I tended to go way too heavy on my weathering when I first started and didn't study enough prototypes, whether in person or in photos, to get the weathering in the right places. I'm just glad there's no wayback machine so you can see some of the ones I did 40 years ago
This an IC ice reefer I completed and weathered a few weeks ago and I'm still trying to get it right:
