Graphically, this game doesn't leave you wanting. The environments, character models and lighting effects all show off the 360's prowess and make the game a sheer joy to look at. The environments have all been updated, but still fit the rugged, technological feel that was set in the previous games. The amount of detail and objects displayed on the screen at one time is just amazing, especially since there never seems to be a frame rate hit.
One of the graphical treatments that really helped to convey the game's feel is the lighting. You will encounter everything from the harsh, bright daylight outside on a desert-like world to the technologically advanced, cool blue rooms of Strogg bases and of course, the mostly-dark rooms and hallways that you will have to run through when the shit hits the fan. Everything from your flashlight to the light generated by weapons fire to the environmental lights just helps to add to the game's graphical beauty.
Quake 4 isn't lacking in the sound department either. Everything from the weapons' fire to the background music helped to sell the game's dark and oppressive feel. When not in the middle of a fire fight, the game's background music was low and brooding, thus adding to the weight of the game as you slink your way through half-lit corridors and rooms with flashing lights.
One issue I had with the audio isn't really with the game itself, or even necessarily the 360. My entertainment setup does not have surround sound, so I am currently stuck with the two speakers built into my TV. It seems that the default setting for the 360 is for full 5.1 or 7.1 surround sound. Having seen what the 360 can do with surround sound -- this is great. If someone is talking to you and you move around, that voice transfers from one speaker to the next. Unfortunately, if you don't have surround sound and you haven't explicitly gone into your 360's setup to change that, what you will experience is conversations fading in and out as the voices move to non-existent speakers. Like I said, I can't fault the system or the game for this. It's just something to note if you don't yet have a surround sound system hooked up to your TV and you haven't changed the system's default audio settings.