SWAT 3. Although extremely dated with poor quality models, it is addictive and fun with high replayability.
The missions themselves are often confusing or puzzling. You find yourself taking down multiple enemies and watching with satisfaction as they get bagged and tagged by your guys. Then you cannot remember the mission brief and have to thoroughly search the map for a hiding fugitive. Many a time you "end the mission" only to find you missed a guy and have to go back.
The fighting system is simplistic, and unrealistic. For example a shot in the hand can kill an AI instantly. Blood effects are poor. The choice of weaponry however makes up for this.
The multiplayer itself died within weeks, nobody ever goes online.
Finally the game is fun at times but often infuriatingly hard and easy to get lost. With modern technology this game runs effortlessly on most computers, and the loading times are excellently short.