35th - System Shock II (PC, 1999)
One word: SHODAN. One of the best villains ever created for any media, and not just videogames, overall. While the game stands on very solid merits of it's own, SHODAN elevates the game to the heights of one of the best ever created. The cliffhanger in the end after defeating her on the virtual space left me shouting at the screen for a couple of minutes when I completed the game, it was that good and nerve-wrecking xD.
While SHODAN's presence makes the game great, it also some other good implementations as well. The mixed FPS/RPG/Survival Horror approach from the System Shock series was pretty novel for the era and on the second game it was vastly improved upon. It's branched character creation, with each class getting unique bonuses at the start also opened plenty of replayability options as well. With the very limited amount of ammunition, weaponry and tools you can accumulate during the game, weapon maintenance (melee especially) was essential for the survival and ultimate goal of destroying SHODAN. 
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
