Delta Force is one of the first open world realistic FPS games. Game was released in 1998 and was developed by NovaLogic. Delta Force used Voxel Space Engine capable of rendering large realistic environments. Graphic does look bad when you compare it to modern games, but at the time the game engine looked very realistic. The player takes the role of a Delta Force soldier completing various missions all over the globe. Singleplayer game was pretty decent at the time, but the most fun part of this game was LAN multiplayer.
This is also one of the first games where players get to chose the equipment before going to battle, typically considering this is a long walk, long range type of game, best choice was to use long range scoped rifles. The inventory had three basic slots, one for the main weapon, pistols and grenades. Every shot was one bullet one kill, the same would happen to you if the enemy finds you. That gave this game the realistic tone, specially in multiplayer. So many times you would camp somewhere and suddenly you're dead. Environment had a real role in this game and finding the right spot would win you the match.