After having beaten the game on the Regular difficulty setting, I have to say I found parts of the game to be both confusing and frustrating at times. The source of my frustration is twofold. First, the A.I. - which many have been critical of since at least CoD 2 - seems to be rather basic in nature, taking only their scripted positions, and never showing any sort of communication or tactical knowledge (flanking, searching, patrolling etc). This problem is worsened when attempting to raise the games difficulty setting, as not only are you not able to sustain as much damage before dieing, but also each enemy makes it their personal goal to kill you (and only you). The second reason compounds the first, that of the blood soaked screen that gets progressively more bloody the closer to death you get. Not only are you unable to sight your attackers, it gets so bad you can barely see directly in front of you, making finding a quick escape route or some cover an impossibility in some situations. The bloody near death screen is an example of a cluttered and inefficient H.U.D. design, as while Infinity Ward wants to warn you your near death, it many cases that visual cue ends up costing you your life. This poor implementation of a low health warning system almost immediately lead me to comparisons between other FPS which utilize far less invasive, and more informative designs. Bungie seems to have mastered the minimalistic approach to a HUD. Their system is minimalistic by comparison, but sacrifices nothing in terms of information available to the player. Visual and audio cues go hand in had, but neither of them overpowers the players ability to concentrate on the task at hand, rather they work to inform you of your current situation as well as that of your surrounding environment.
Anyway contrary to my above rant I have actually enjoyed both the single and multiplayer a great deal. I just feel that the game could have been greatly improved had they fixed the issues with A.I., HUD design as well as making some of the enemy encounters a bit more reasonable.