Look carefully, they are there. Those are my interpretations of a successful formula. Making a map is easy, making it play well, is tough. Making a classic is pure chance. Intentionally throwing in some imbalance and leaving the player more freedom to choose his path, the chance can be multiplied.
Sterile maps play, well, sterile.
Yet, there should be some slight imbalance thrown in. Whether that would be an extra item, a powerup or a place to camp, that's up to the author to decide. Tipping the scales in this manner is the driving force of the action. Make some items more quickly accessible using an advanced method like strafe or rockect jumping. Never make a significant item accessed only in that way.