There's a pastime I hold dear to me, not speedrunning or even one gun runs, but no damage runs for shooters. There are two games that I cannot do the run with, Half-Life and Deus Ex. I'm sure it is possible but, I'm in awe from beginning to end because of the quality of the game. I'm distracted and therefore, get hit within the first two hours.
Everyone knows how a shooter works
Step 1: Take gun/crowbar
Step 2: Aim and shoot
Step 3: Tea-bag enemy/enemy gib
But Half-life has a bit of platformer integrated in the game. Long-jumps and precision jumps can be found everywhere as well as the infamous endless PIT OF DEAAAATH. They kill you at every opportunity. Once you get past the jumps, enter enemies. Either the special forces or the alien creatures, or even ZOMBIES. Get past these guys and you have bosses that can only die after you solve a puzzle. One of the bosses requires you to throw grenades into a pit, have it temporarily retract and get down to the bottom of a room. Add one hit kills and valves, and you have the average boss fight in Half-Life. Also, did I mention you start off with a crowbar. Did I have to, we all know Gordon's best friend is the crowbar.
Well, to be fair, he also has other friends in high places (literally if they run into barnacles). Scientists who provide health and guards who provide, cover fire. By the end, you don't need them because, well you have enough weapons in your repertoire to form an army. Alien and human weapons are needed to get further into the game, and like any other shooter, the pistol will always be full of ammo at the end because you tend to only take out the shotgun or machinegun.
If you haven't played Half-Life, what the hell man. It is one of the best games of all time.