Killzone 3 and Bulletstorm are dropping this week, and if previews of the games live up to the hype, they both may secure a berth in the still-young First-Person Shooter Hall of Fame. The genre is one of the most popular in interactive entertainment, churning out household names like Halo, Half-Life, and Call of Duty, and continues to rake in billions of dollars for the industry every year. But why? Why does the appearance of a hand holding a gun on-screen change the way we feel about a game? Why does that genre in particular strike developers as the go-to choice for many of their titles? We're not smart enough to answer such questions, so we won't try. Regardless, this week's double-dip makes it the perfect time to take a look back at our 50 favorites from the genre's 20-year history (Catacomb 3-D came out in 1991). From the simple PC days to today's elaborate theaters of war, here's a run down of the best games through the eyes of you, the gamer.