Performance on 2010 21.5" iMac I3 pretty poor
Working with Trainz support I had to dumb down scenery, trees and texture graphics to just "Normal" and drop distances to 2500m from 5000m. Now the graphics are "almost" smooth in dense city scenes. Now it just looks like a table top train set. Very good game physics but I expect that since I had the older Trains sims for Windows years back. They do have a ton of free add on content. I have the std 4GB RAM, 3.06 GHz Intel I3 CPU and the 256MB ATI Radeon HD 4670.
Trainz support says a future update will have some performance tweaks in it. I may try adding more RAM since I'm stuck with the graphic card. If you have only a 256MB graphic card you might want to hold off on getting this sim till the update comes out and see if it makes a lot of difference. I'll update this review if I add more RAM.