It's very easy to slip down a cliff or into a pocket that you can't walk out of; there should be an unstuck button that pops you to a "safe" respawn area (maybe near the car or screens) so you don't have to quit the game, as there doesn't appear any other way to get out.
In singleplayer: I found quite a few items (5 orso?) and deposited them, however while playing there was never any kind of encounter with any kind of entity. I'm not sure if this was intentional; I didn't manage to find all the items or guess whose body was out there correctly (I couldn't find any Staff chips or what the tiny key went to, or flare gun, etc, and there were no more doors to interact with anywhere.. I kinda gave up after a while as it wasn't very engaging). I was expecting a chase sequence while looking for the items, so maybe this isn't a bug but intended.
On medium settings the game ran well, there were a few pop in issues with things like boards over windows.