Another well-made game by Infinity Ward. Nice to see a change in setting as well.
Gameplay: In both single- and multi-player the gameplay is similar to the previous games of the series, but there are key differences in both. In single-player, the two playable story threads are interwoven into a single campaign, rather than the concurrent but separate campaigns of previous games. Multi-player is a lot different too, with addition of a hardcore mode, as well as upgradable weapons, configurable classes, kill-streak awarded support powers, and most importantly, perks. These perks tend to award the players slight advantages with different things, but they are arranged into three slots, with perks grouped into these, and some perks interfere with the rest of the class loadout. Another change in the gameplay mechanics with this game is that most surfaces are now penetrable to differing degrees, and the amount of penetration capable differs between weapons. This forces players (especially in multiplayer) to constantly re-evaluate the effectiveness of their hiding place. Unfortunately, as the game appears to have been designed with consoles in mind, the multiplayer maps are rarely large enough to allow large-scale strategies, and the pace in larger servers is generally quite fast.
Graphics: Overall, the graphics in this game are of a greater quality than its predecessors, yet still accessible to lower-end computer set-ups. Unfortunately, its sequel (Call of Duty: World at War) didn't appear to share in this. As is typical to Call of Duty, almost all the in-game movies are interactive, and even then they are rare. Interestingly, CoD4 scrapped the notepad briefing loading screens for a movie version. I find that this makes the loading sequences more engaging than tedious, as the level usually finishes loading before the movie finishes.
Audio: I've been a fan of the musical scores that accompany CoD throughout the series, and this CoD is certainly no exception. The scores are subtle, but usually kick in at the right moment, adding to the atmosphere of chase sequences, or making that in-game movie that extra bit more gripping.
Other: Overall, I greatly enjoyed this game over the past few years of playing it, and I look to its (proper) sequel with great anticipation. This game is certainly worth the money, especially when it reaches the bargain bins in the not too distant future. The multi-player experience in my mind is only shadowed by that of Valve's games, but being second to Valve's games in terms of multi-player should really be considered high praise indeed.