It looks really good. The detail in the appearance of all the weapons is absolutely outstanding.
The sounds really killed it for me though. I'll be honest, I didn't really notice it to much until I got to playing with the weapons I own or have fired in the last few weeks (yes that probably makes it seem a little worse than it is from my view point) but after that I did start to really notice the lack of detail in the sounds for everything. Maybe not so much the lack of detail, but more that lack of variation between calibers (or pretty much anything with the silencer). I understand not having a "proper" sound effect for every single weapon, specially not with this number of guns, but some really could use a more aggressive firing sound than others.
There's also a few times, during reload, that you can see the clip come up into the breech before ejecting. Not a huge issue, it doesn't last long and only really stands out if it lags a bit. Just wanted to point it out.
Please don't think I'm just trying to put this game down, or that I'm trying to act like some kind of badass expert (which I am most certainly NOT) and nitpicking the little stuff. I'm really not trying to do any of that. Its just that with this level of detail in how it looks and works, I guess it just makes the things with less detail stand out more. Just my two cents, please don't take it as an insult.
Lastly, nice touch with... well everything in the menu. Optional attachments, timelines, simply put, yes everything, including the setting menu. Its really just great.