A bit of a re-hash of MW2. The game feels more like an overpriced expansion pack.
Graphics:
The graphics in the game have only had a minor change from Modern Warfare 2 as it runs on the IW 5.0 Engine. This is just a retouch of IW 4.0 which was MW2's engine. So the graphics haven't changed overly much and are admittedly starring to fall behind the rest.
Sound Design:
The game still has a considerably good sound design and the game still sounds good. But it isn't really the best sound effects you will hear in a video game. i.e. The sound of a grenade is a bit underwhelming when compared to the sound from some other games.
Multiplayer:
The game's multiplayer is still the same basic mechanic with the same basic modes and the addition of some fun new ones like "Kill Confirmed". It hasn't changed overly much and will please most fans of the Call of Duty series. Although a good improvement is that Second Chance no longer runs rampant. Another good addition was to enable players to edit the game modes themselves. The leveling up system has been changed and it helps the player grow with their preferred weapon which is a good addition. The "Points Streak" system doesn't feel overly fresh and it feels like a more selective version of Killstreaks. Also the player's arsenal hasn't changed very much either part from some removals and a few new additions. The maps still do feel small and in some cases smaller then MW2's or Black Ops' maps. Overall the gameplay still offers a fun and fast paced experience but it is feeling pretty lazy in that the developers said "We want to make an evolution not a revolution" and it feels more like a revolution.
Singleplayer:
The singleplayer hasn't changed much either. Infact it hasn't changed too much since COD 2 apart from some small gameplay additions (e.g. Chopper Gunner and Quick time events) It is still pretty fun but feels like it has just been over done. But one thing that will appeal to pretty much every fan is that EVERYTHING blows up. Even the Eiffel Tower. There isn't really much to say about the single player apart from it's been done.
Spec Ops:
The Spec Ops mode has made a return but with a new survival mode. The survival mode is very much so fun and feels pretty fresh. It is honestly one of the main reasons to purchase this game as it is the most new and fresh feeling piece of content. The ability to play with your friends and wipe out wave after have of enemies or hit a Juggernaut in the head with a predator missile very much so fun and appealing. The ability to purchase new guns and equipment is entertaining and the fact that it happens both in solo and multiplayer (quite like In Rainbow Six: Vegas 2) means that you can catch up with a friend easily or just get yourself to a stupidly high level quickly.
Overall Modern Warfare 3 doesn't have much to add to the ever growing world of the FPS and is feeling pretty old now. The game hasn't evolved very much and it is showing the signs of wear. It is still a fun game but it feels more like an expansion than anything else, so if you wish to purchase it, I would recommend trying to find it at a cheap price.