Gave the game a try recently, and how fucking dark everything was fucking drove me nuts. I knew I wasn't fucking crazy when I thought "this is too dark, I can barely see a got damn thing!". Especially when I went to adjust the brightness setting and it did diddly dick.
Let's just say I gave up on Deus Ex pretty quick. The above issue was bad enough, but when the opening level of the game tries to insist "stealth" and "guns blazing" are equally valid options, only to die 20+ times on a casual difficulty trying the latter and to have the former just flat out not work constantly, my patience wore thin very, very fast.
It doesn't help the stealth seemed really hit and miss as is, sometimes I could literally crawl right underneath someone's nose and they wouldn't notice me, others I could be completely fucking hidden except for a pixel 50 feet away, and they see me. Never been a fan of stealth games, but I sure as shit don't have to patience for one that up and decides when it wants to work.
Don't even suggest to me "gun blazing" is viable when I can be 1 shot by an enemy when my head is a fucking pixel in their view. It would of been way less insulting if right at the start of the game there was a big sign that said "fuck you, this is a stealth game, don't try anything else, faggot".