Well, lets put it this way, BK Vissers
TSW = good looking graphics, not so good simulation realism, more like arcade gameplay. Pre-set scenarios, you can't really personalize anything at the moment. The only possibility you have as in terms of gameplay is to drive the train, travel as passenger or just watch trains go by. You cannot control trains as a dispatcher.
Run 8 = Graphics are similar to MSTS from 2001, excellent simulation realism, great realistic gameplay and train physics, possibility to also play as a dispatcher ( controlling signals and junctions ), possibility to work on big freight yards including humping operations, has multiplayer, you can also do some railfanning in-game. You can create your own train and leave the AI drivers take the train till wherever you want it to go. There's so many more things to it...
Hopefully this gives you an idea of how does it compare.