Conceptually sound but too rough to consider except as a WIP
First a list of things I quite appreciate:
The standard ballast texture, if it could be made to tile better
The idea of grades of ballast and the stained ballast node
An attempt at modular overhead line equipment
The mast truss
The idea of cable troughs
However I find the art a bit inconsistent and there are a few assets for signs that may have been copywronged from railsigns.uk, despite being attributed (the author should recall that in the absence of a licence statement, copyright remains all rights reserved). I also think the author missed a big opportunity to use display_modpack for the plethora of 'Stop \<color> of \<x> cars' signs - simply allow writing two numbers in a formspec attached to the sign. Then only one sign node definition is needed per colour. A consistent font or small set of fonts and texture resolutions should also be used instead of a mix of pixel and smooth fonts. Some signs also have a very tiny size in the world, which makes them illegible from more than about half a metre away, yet they still have the same size selection box. Others have a very high resolution which causes a big framerate drop whenever they are wielded in-hand; a separate in-inventory image can address this.
The overhead line equipment, or as it's referred to in-game "OLE" without explanation: I like the idea of modularity in height and flexibility of track spacing. However, the lack of any wire at 30 and 45 degrees to match the track is a bit dissapointing, even if it would take a lot more to implement. Also, this is not actually the first attempt at OLE for Advtrains - MBB actually made a more basic system back in 2017. Although the britsignals OLE is more complicated and a bit thinner on the wires (which is usaully more desirable), the MBB mod actually manages to get a better colour contrast including darker cables and has a separate messenger/return wire .