Hitman and I had a discussion about how darker hydronex1 is compared to hydronex2 (which is normal as N.K. likely has improved lightning and such).
I thought it could have been due to patch085, however after I removed it walls are still quite dark.
IMO it's playable even if that dark, it's only the lateral walls. I can't confirm something changed.
Hitman, if you can do further testings ...
Note: you may pay attention to the lightning chosen (vertex or lightmap) knowing that some server will switch you to lightmap because of videoflags variable.