1. Call of Duty 4 - Mile High Club
I'd be amazed if somebody owns an Xbox 360 and hasn't heard of this achievement. Back when Call of Duty 4 was released, this was the marker of success in the game. Unlocked as a post-credits bonus mission, Mile High Club sees you playing as an SAS officer, tasked to save a hostage held during a plane hi-jacking. On lower difficulties, it's a cake walk. On Veteran, it's a whole different story. It requires correct placement of flashbangs and a whole lot of extra luck on top to get through this plane in the time limit. I don't even want to consider the amount of times I got right to the end and accidentally shot the hostage either. Admittedly, there are harder achievements out there now but none are as iconic as Mile High Club. Even now, people are still seeking ways to earn this as fast and as simply as possible. A highly rewarding experience, Mile High Club is an achievement that everybody needs to earn before the Xbox One arrives.
There's thousands and thousands of achievements out there and I've undoubtedly left a couple of important ones. Let's discuss those in the comments below.