


Gameplay video: http://www.youtube.com/watch?v=PRiLoJ4x5j0
Perfect Dark 64 was a revolutionary shooter for its time. While the multi-player didn't quite match that of Goldeneye 64 in most regards, the single player and weapon selection is where it stood out. It is still mimicked to this day in many of the weapons and FPS gameplay concepts it introduced, and Halo's weapons are based heavily off of mechanics which Perfect Dark 64 established. It also pushed the N64 to its max in terms of hardware rendering, and looked great for its time (though it is now hard on the eyes).
In terms of weapon choice, the player could choose between various human and extraterrestrial weapons ranging from scoped pistols, to alien sub-machine guns (Mauler -- inspiration for Halo alien weapons), guns which transformed out of laptops, alien machine guns that could release their clip on one click, automatic shotguns, alien sniper rifles that could see body heat through walls, and even blender-like grinding melee weapons (Reaper).
The story was also somewhat compelling, and the gameplay was superb. The co-operative play worked very well, and provided hours upon hours of fun.
Wireframe:

Wireframe Breakdown:
1. Ammunition in clip - this is always visible on the screen, and at full bar, it is filled to the maximum amount of ammo you can fit in one clip. As you shoot it decreases, when you reload, it fills up.
2. Ammunition total - also persistently visible, and it displays how much total ammo you have for the selected gun. It depletes as you reload (by a clip's-worth of ammunition), and is filled up as you pick up ammo on the ground. There is a maximum number of bullets that you can carry.
3. Gun mode status - displays as a solid red vs. yellow box depending on what mode of firing your gun is in. Each gun has two, and yellow is the secondary/special state. As you switch, letters come out and slide to the left to tell the user what each state does.
4. Text display - alerts player of things like ammunition pickup, shield pickup, gun pickup, or anything that needs to be conveyed through text.
5. Weapon being held - off center, aimed toward the middle point of the screen (6)
6. NO CROSSHAIR - I believe you are able to turn it on, but the good players play without it, and because of the way the gun (5) is angled, it is not too difficult to know where your bullets will be firing
The GUI/HUD has a very square/sharp look to it, which is holistically integrated - text, shapes, and layout all seem to add to this.