Since CoD3 was developed by TreyArch and not Infinity Ward, a fact Grant Collier is quick to point out, the team has had plenty of time to ensure CoD4 will return the franchise to its former glory.
I think the move to provide both types of RPG elements - those that persist throughout the players 'career' ala Battlefield - and those that are round-based such as those offered in Enemy Territory - is a smart move. EA and DICE really tapped into something with Battlefield, and improved the formula in Battlefiled 2, with the RPG elements. It creates this MMO-like fervor to continually check your score and see how your progressing towards that next 'level' - without the commitment an MMO requires.
A Return to Duty - Multiplayer Preview
I think the move to provide both types of RPG elements - those that persist throughout the players 'career' ala Battlefield - and those that are round-based such as those offered in Enemy Territory - is a smart move. EA and DICE really tapped into something with Battlefield, and improved the formula in Battlefiled 2, with the RPG elements. It creates this MMO-like fervor to continually check your score and see how your progressing towards that next 'level' - without the commitment an MMO requires.