QUAKE 4

Here is a link to a playlist of every level completed on General difficulty. Simply follow what this guy does, and you should be able to get any of the difficulty achievements without much problem.

*NOTE*
Save often. It'll really make this game a less of a pain if you're not replaying the same few minutes of the game over and over.

http://www.youtube.com/view_play_list?p=4BFB72AC7795CECC

Not bad quality too, considering the game!

His run is about 4 hours, which actually doesn't sound so bad considering the ratios on these achievos.