In my opinion, the biggest issue on SEHS is that the lower level of Ebbsfleet station is not usable. If it was usable, there would be more drivable Javelin services. And in future DTG could develop a route from Ebbsfleet to Ashford if the lower level of Ebbsfleet was usable. It's a disappointment that it's not usable. And the HS1 between St Pancras and Ebbsfleet runs mainly in tunnel, which makes it a bit boring to drive.
I’ve only done the tutorials so far but yeah the ballast isn’t really realistic at all. Looks laid stone by stone, raked over for smoothness and sprayed grey. I noticed it especially when leaving London in the opening tutorial
They did try to adress it because of all the all the complaints about the ballast however it seems that they just resprayed it grey. It's a bit better from before but still unrealistic for a sim