The 1-player campaign mode for Doom 3 may be to terrifying to take on alone, but the co-op is completely awe-inspiring. I noticed that the changes were quite significant; not only was there a lack of PDA or Soulcube, but there were many, many more enemies, and the game was quite a bit shorter. There were also different boss encounters, it seemed.

The basics of the Doom 3 co-op were very well thought-through. The dropped backpack idea was neat, and, thankfully, the co-op wasn't like Dynasty Warrior, for example (it wasn't game over if one of the two died). It was particularly horrifying when your companion dies and you are trapped in a very dark area, awaiting his return.

Overall, the co-op mode was VERY good, and I understand why it requires a system link to play (the graphics are so advanced, the Xbox couldn't handle both screens on one TV). It was a bit aggravating when we had to go out and rent another copy of the game, and get a system link cable.