this video has the 'top 10 video game weapons according to gametrailers.com'

https://youtube.com/watch?v=GxSdKF5Fd38

They really should have put the Wraithverge from Hexen (another good game, which was quite special using the 'hub' system)
http://doom.wikia.com/wiki/Wraithverge

it's one of the best weapons I've ever used, required a lot of mana to use, but it was so destructive, when you fired it, 4 ghosts split out quickly to find enemies nearby, (they did it automatically like 'heat seeking misses') if they found the enemy, they would very viciously rip into the enemy killing/trying to kill them