There are two philosophies in making an excellent FPS.
If you're going to make it an action packed thriller epitomized by COD 2/4, then you must pay attention to pacing. Both COD 2/4 and UO were masters in this, and it showed.
If you're going to make it more open ended, then you have to create alternative routes, a reward system for exploration, and customization but while giving the player a good idea on where to go. Think Deus Ex/Bioshock/Half Life 2 for this.
If you're going to make it an action packed thriller epitomized by COD 2/4, then you must pay attention to pacing. Both COD 2/4 and UO were masters in this, and it showed.
If you're going to make it more open ended, then you have to create alternative routes, a reward system for exploration, and customization but while giving the player a good idea on where to go. Think Deus Ex/Bioshock/Half Life 2 for this.