Call of Duty: Modern Warfare is an excellent game with online and offline play it comes with four difficulty levels of play and it recommends the level of dificulty for you after the training level. The online play is excellent and realistic with options for choosing weapons and add ons with challenges to be completed. Another good point is that all of the achievments are got from offline play so if you don't have xbox live you can still get all of the achievements.
For all of you who like looking for glitches and playing with them there is a unranked private math section where you can increase your jump with old skool mode so that you can search around the map for places usually unreachable.
Excellent game and I would reccomend it to everyone.