What the best shooting game their is

This is a very opinionative question, and also more details would be good. What platform, FPS or TPS, etc. The Halo series is for XBOX/XBOX 360 with Halo Combat Evolved/Custom Edition and Halo 2 Vista available for PC, these games are considered some of the best by many. If you want more realism try one of the Call Of Duty games or possibly America's Army for PC/Linux/Mac.