It's fairly self explanatory............
Decent weathering: Like I said decent, I've seen much better from un-paided people. I expect much higher than freeware, for a $60 (or so) game, from a large company.
Extremely poor modeling: for what they are, there are many areas that need more polys, and just as many, if not more areas where polys can be saved, many Trainz freeware exceeds MSTS2 quality, and at least from general looks, without sacrificing performance.
Out of scale: Having the plans to the GEVO, and the SD40-2 In a rough comparison the models are extremely poorly measured, short in some areas, long in others. Out of scale is out of scale.
Yes the Auran default content is old, we've been through that. But it was also made with the original version of Trainz, which at the time was the best it could do. It's unfair and unbalanced to compare Trainz default with MSTS2 default. Why? Trainz while it has evolved and has much higher quality content (SPORBUST as an example with his SD40-2's), MSTS2 is starting from SCRATCH, not building off of previous models. You can't compare an evolved sim with a new sim. If you must compare two, compare KRS with MSTS2 (which btw suffers the same problem in both programs).
And FYI the MSTS2 SD40-2 looks like a blind 4yr old made it.