It just wasn't dark enough. Not plot wise, that was pretty dark. But even the night missions felt there were 4 full moons out. I was really surprised that the Golden Cat mission was during the day. It's cool that they tried something new, but I don't think it was as effective.
Well, I guess I have one more complaint - the dark sight was way over powered and should've taken more mana. It was a little like the Detective Mode in Batman: Arkham Asylum. Deus Ex HR's see through walls mode was a bit better balanced
All this said, I've enjoyed the game and am thrilled to see a game like this made. I love both creators' past work (Arx Fatalis was a great underrated game) and hope they can keep going. I think Thief 4 is in dev by the team that did the latest Deus Ex. If they can do as good a job with that reboot/modernization, I will be one happy soldier.