One of the best games I have ever played, simply Stunning.
Good storyline, engaging characters, great immersive Sci-Fi feel.
Amazing weapons that feel like the have "oomph" to them when they fire and enemies that you can't wait to abuse them with, very satisfying combat in later levels.
This game starts off slowly and then builds, like a good movie. It does not start with insane combat, but it builds and the insane stuff hits later. Some of the best firefights in a game ever.
Varied level design with great attention to detail.
Amazingly designed enemies, amazing sound, amazing facial animations.
Great graphics, now of course they are not at the level of a high end PC, but how is that a fair comparison? Compared to other Xbox games, amazing graphics.
Do not be let down by people complaining of frame rate issues, they do not interfere with the gameplay at all, yes here and there there are some drops, but nothing to worry about at all, played well from beginning to end.
One of the best games I have ever played, next to Half Life 1. Here's hoping for Half Life 3