HUD is a requirement If you like playing casually with the HUD turned on and don't look at anything in the locomotive itself, this is probably not an issue, but some of us "hardcore sim players" like to play without HUD so it's quite important to keep the game playable that way. Most locomotives are missing implementations for systems that are required for the train to operate in real life like train length buttons and timetables. These systems can be substituted by the HUD but some people just don't want to look at it. System downgrades are forced Implementation of most systems is very simplified. For example train length button does not require information about the train's length and AFB does not require any of it's five parameters. I'm not against trains automatically managing certain systems but it should be optional. Inaccuarcy causes confusion This is currently limited (at least as far as I know) to the Taurus where you almost can't tell if the locomotive is powered on or powered off. I know this thanks to the official manual. What is not known was never there These are mostly visual things like bios boot screen (which I like a lot) and welcome pictures which are not implemented because people don't know that they are there.