I'd throw Hunt:Showdown up there. I started with a friend a couple years ago and we just devoured YouTube videos to learn tidbits. But I realize not everyone wants to watch people playing a game in order to learn and play a game themselves. I'm still constantly in awe of the sound design and how it meshes into finding intense gunfights and defines how you engage other players based on what guns you think they have based on sound versus what you know about your own loadout. Each fight I'm learning something new and I'm a little over 500 hours in. I think the "generally accepted" amount of time to get decent at the game is around 1000 hours.