Forgot to reply to this - as always, thanks for taking the time to play/critique my game!
I believe a good handful of issues you've mentioned have been fixed since Demo Day, but always good to have the input.
I'm trying to figure out a good solution to the V-Sync issue, as I almost exclusively playtest in the Editor and I have V-Sync forced off on my machine I hadn't noticed any of these issues with input lag or weapon sway, so I'll be working on figuring out how to add a V-Sync option to the game.
As far as the item descriptions go, there are brief descriptions written in the engine but I hadn't gotten around to finding a nice way to display them when you hover in the shop.
The shotgun is just super buggy and terrible at the moment - I really should've omitted it from the DD28 demo. Even when it's working properly it's not balanced at all.