Nail gun kills in one shot to the head if you hold to charge it. At least it did for me (blue or purple version). But yeah other guns are a bit erratic and accuracy is meh. If they weren't it would be super easy on top of it being fairly easy as it is now. The only hard combat area in the game is the last bit where it will spawn like 50 guys if you get detected. You'll probably hate that bit like me. 80% of my kills were using the shotgun since it does a good job. I hate how little ammo they give you and most guns just feel too loosey goosey. My favorite thing about combat was hacking turrets and setting them for baddies.
I finished it in 13.5 hours. Stayed repetitive all the way to the end, although there are a few secret areas you visit in the last few hours. But to unlock them you might have to redo the same bit a few times so in some sense it gets even more repetitive. I screwed up and had to go around the loop a few extra times to get it right. I also fell to my death on the last level after killing all targets but just hit alt+f4 to save myself from doing the whole ****ing day again because it's tedious.
I think it's odd that the game doesn't give you direct instructions on how to kill all 7 in the one day when it seems to give you direct instructions for almost everything else. I guess it expects the player to work it out? Might be hard to complete if you get to the final stage and then take a break for a few weeks. Sure it's not super complex but the way things are arranged in the leads page could make some people confused.
The Colt+Julianna chats get more annoying later in the game imo and the story is pretty bad overall, no pay off there for me at all.
Overall I thought the game was mediocre. Too repetitive. Levels are not that big or interesting. Stealth is okay but it has some quirks. Shooting is mediocre. Julianna incursions are annoying (still happens in single player). I think it has a few cool ideas and might have been okay as a 7hr indie game. 5.5/10