I'm a little drunk... so this will likely be somewhat unfocused. 
 
I've heard people bitch about monster closets ever since Doom 3 was released. The strange thing about that, the only game that really has seemed to have been "tarred" with this moniker has been Doom 3.  The thing that blows my mind about this, is that monster closets have been around for years... and long before Doom 3 was ever released. 
 
The real question I supposed would be, "what is the monster closet?" An excellent question. In reality... this device is really meant to be an area just outside of the player's range of vision that spawns enemies for them to combat. Every game ever made uses this tactic... from top down shooters, to real time strategy games. The developer needs a place to spawn enemies to attack the player from a position that they may not be ready to engage from. So... why does Doom 3 get tarred with this designation? 
 
The answer is that the developers didn't bother to paint a door on the wall of the location that certain enemies spawn from. Despite the fact that games Rainbow Six Vegas, and Ghost Recon both use this tactic, they get a 'get out of jail free card' because they decide to paint a useless fucking door on one of the walls of the monster closet. 
 
It's entirely possible that I'm crazy (and I invite you here to rebut this argument), but it doesn't make any sense to me that a game like Doom 3 is maligned for picking scary times to spawn enemies as being for having 'monster closets', while games like Serious Sam and the upcoming Serious Sam HD have absolutely no comment on the matter (especially since people are still bitching about it over new screenshots for RAGE). 
 
Give me a good argument for why monster closets in Doom 3 are bad, and why they are awesome in games like Ninja Gaiden and Ninja Gaiden 2.