Most first person shooter games are now integrating several common things into the games. The common features are game play mechanics, which allows for better game play. The features that are most typically copied are allowing sprinting, as well as the shooting mechanics. These two features are copied because game developers will copy what is popular. This is not to say that these features are bad; in fact I would say that games having similar mechanics is a good thing if players want to do well.
While Call of Duty has been giving players the ability to sprint for a long time, Halo is just now integrating it into its games. Halo: Reach allowed players to sprint, but that was an item that had to be picked up in order to sprint. In Halo 4 the player can sprint at any point with out that extra item, giving all players more mobility. Providing players more mobility gives the game a faster feel to it, which can make the game more exciting.
Shooting mechanics are the most important thing to a FPS. The shooting mechanics that are most often copied from game to game are recoil, dispersion, and the zoom functions. These features are universal when it comes to guns; meaning that every gun is different and will react differently. But in the early stages of the gaming industry, all guns reacted the same, meaning they shot straight in a single line. In the recent generations of FPS games, there is such a wide variety of weaponry that the player can use that to build in the aspects of recoil and dispersion that have become very important. The final thing that most games have started copying is zoom mechanics. With zoom mechanics, recoil is reduced and the dispersion rate is also reduced. Again, Call of Duty has been good about using this mechanic for its games, as they are more realistic then say, Halo.
But features are always going to be copied in the gaming industry. This is going to keep happening as developers pursue popular trends. Since Call of Duty and Halo are the top games, they will be the games that are copied first. However this is not to say that copying is a bad thing. Copying weeds out all of the bad features because there is no point in copying a feature that is unpopular. Although there needs to be some innovation from some people, every game will be exactly the same without it.
Copying game features is nothing new to the game industry. Sprinting and shooting mechanics are the biggest ones that come to mind right away. They are simple things that make the games much more fun when done right. The industry will keep copying each other while still having some innovation, and that copying will filter out the bad features. Copying will persist, which is not a bad thing as long as some games are different.