3. Supply Lines - Grand Theft Auto: San Andreas
RockstarPrior to Grand Theft Auto IV, the GTA games boasted a fairly high level of challenge, as evidenced by what is regarded by most players as the most difficult mission in any GTA game, Supply Lines. Though it thankfully happens to be optional, the mission revolves around CJ piloting Zero's miniature plane to destroy five of his enemy's couriers, and then flying the plane back to Zero's roof. What makes the mission so tough? It has a brutal fuel limit, and running out of the stuff before returning home results in an insta-fail, so players need to be ruthlessly efficient with plotting their route to each courier and quickly taking care of them. Most of us no doubt spent hours trying to beat this stupid mission, and while it wasn't necessary to beat to complete the game, it was vital for those of us who wanted that esteemed 100% completion rating. Was it worth it in the end? Probably not, but the sense of reward and relief when it was done is undeniable.