COD4 is a brilliant game with an intertaining single player mode and the best multiplayer of any game on the market!
The single-player game mode is amazing and will leave you wanting more if you stop halfway through. It is intertaining all the way through and really gives you the feeling that you are there. Each mission is pretty short (about 20-40 mins. each) but there is a large number and variety of missions. The AI are very smart and actually use their brains to try to kill you. Never will you have a moment where you think to yourself "Oh, that was dumb" There are many difficulty levels to choose and the easiest will have you breeze through the game with very few deaths. The hardest difficulty level is ALMOST impossible. I have beat many of the missions on the hardest difficulty but cannot manage a couple of them. It is a real challenge and will keep you busy for hours.
The multiplayer, belive it or not, is even better than the singleplayer gameplay. It will keep you intertained for days and days of gameplay. There are many strategies you can use and being able to customize your abilities, weapons, and weapon loadouts allows for you to personalize the gameplay even more. There are a huge variety of different maps and locations. Every weapon is tuned perfectly and that includes weapons like the grenades, claymores, C-4, and many more aswell as the guns themselves.
This is one of the best games of all time and will keep you intertained for months. Everything is perfectly designed and flows smoothly. It was a great idea to bring Call of Duty to the modern era and I hope Activision continue on this trend of making AMAZING first-person shooters!