Not so good....
Graphics: GBA is better suited for MMORPG-ish Anime graphics, this game looks pretty blocky and will feel hard on your eyes with its few textures.
Gameplay: Every level looks almost identical with its white floors and white or blue walls. Almost all levels are mazes. The A.I. is nothing special. They stand and shoot, you shoot back, done. All of the 5 to 6 guns use the same type of bullet so all you have to just do is pick up ammo.... The enemies are usually Nazi's of differing ranking (or dogs) and toughness but sometimes you end up with a boss or mutant, just do what you always do with them and shoot. The turning radius of your character is terrible and you will find yourself having trouble trying to do the only thing you can do, shoot ! Whenever you get shot your screed turns red, but sometimes the screen will flare up with red to a point of blindness and you need to wait a minute or so for it to clear up. There are hidden treasures the game throws in to make it a bit more interesting.
Sound: Really bad, gun sounds, enemy sounds, doors opening and picking up items are the only things you will really hear, no foot steeps. The enemies are shout the same thing when they see you and shout the same thing when they die (except for the brown guys)
Value: Don't buy it unless you collect games or some weird crap like that.
My Tilt: If you can still FIND this game, yet alone buy it, I would be impressed. But if you still play a GBA and you want an FPS for it, just get DOOM or DOOM II. Hell, just get like a final fantasy game or Zelda or something like that, those are the only game really worth playing now.