I've always been a PC gamer, primarily Flight Sims and FP Shooters. Back in 2001 a battlefield simulation called Operation Flashpoint was released, my avatar is the cover photo on the box. In contrast to heavily scripted games like Battlefield, COD, etc. this product featured huge maps with the ability to go anywhere, do anything, and a with a high level of realism in terms of difficulty, (simulated) physical stamina, weapons and ballistics. There was a campaign but what really made this stand out was the mission editor giving a large degree of freedom to create innumerable senarios with varying environments, terrain, equipment and opposing forces. I've had many many hours of fun playimg coop with my son over the years. Today it lives on as ARMA 3.
Fun fact: this product is a limited version of VBS (Virtual Battlefield Simulator) used by the military by the same software developer.