I haven't installed it but that's one of the very consistent, first complaints everyone seems to have with the mod (among many others). I checked a few gameplay vids on youtube to have a look, and sure enough, it is way too dark. It ruins the game. What's worse, from the threads and comments I've seen, this has been a problem since the very beginning, and complaints about this were flooding from even the beta stage, before the mod's official release. But the dev(s?) just constantly ignored them.
Anyway. To their detriment. I was considering it but have decided now not to bother with this Revision thing after all, even for free.