Call of Duty 4 on DS obviously can't be identical to the game on Xbox 360 or Playstation 3, due to the systems limitations. Fortunatley, the developers had the smart idea of following the allied troops, the ones that cross over with the console versions of the game. This means that there isn't a consistant story, as you keep changing from unit to unit, who have nothing to do with each other.
First of all, the graphics are great considering they are on the DS. The whole game is in full 3D and every person in the game has full voice acting, which isn't seen very often in DS games. The explosions look a bit pathetic, but the characters and levels look very impressive.
The controls are really fun to use. The D-pad or those buttons with the letters on them (I can't remember their names) are used to move the character around, while the stylus and the bottom screen are used to move the camera around, altering your perspective. It is a bit awkward getting used to the controls, but once you get the hang of them they are really effective.
Multiplayer isn't as fun as it is on the console versions. You can't use wi-fi to play over long distances, though you can play together if the two DS's are in the same room. Once you are in the multiplayer mode it is pretty much just a plain deathmatch, hunting down each other to see who gets the most kills.
Overall, it's a really fun game with lasting value, but the multiplayer really lets it down, which is why I am only giving it 4 stars.