I'd say that this game set a precedent for first-person shooters, and was probably the inspiration behind the now extremely popular Battlefield Bad Company 2. Delta Force 2 is the first game to include bullet trajectories, that is the arcing downward of bullets fired at a target some distance away, and many of the gadgets and technologies so ubiquitous in modern titles first appeared here.
There are numerous shortcomings: the graphics are arguably quite poor; and even more frustratingly there a quite a lot of bugs. But in spite of the bad things it is a surprisingly well designed and broad game. The environments are enormous, and you can spend hours marching through hills and swimming rivers, all while listening to the sounds of the wind blowing and the occasional cries of wild animals and birds.
Probably what I like most about the game is the fact that it is about as real and life-like as a shooting game is ever likely to get. Mostly the missions involve rescuing prisoners, or taking out enemy camps, which are nearly all followed by a race to the extraction point to be picked up. More importantly, too, you aren't alone fighting your way through the wilderness; Alpha and Charlie teams often provide overwatch and can actually hit targets, something which AI in modern games can't even achieve. Taking out buildings, tents and enemy ships with laser designated fire missions was something quite fun to do as well.
This game is fantastic, and I still play it today.