The best replacement for doom is quake.

The best alternatives to doom are rated as following:
★★★★★  quake
★★★  iron man
★★★  magneto
★★  doom 2
★★  duke nukem
★★  thanos
★  wolfenstein 3d
★  demolition
★  darth vader
★  ultron
★  lex luthor
  loki
  apocalypse
  lyrics
  gloom
  wolfenstein
  fantastic 4
  duke nukem 3d
  bane of agony
  agony
  mf grimm
  bkb
  rockers
  curse of agony
  justice league
  ultimate doom
  def
  thing
  bloom
  curse of elements

Your alternative for doom is not listed? Suggest!
Speaking about doom, one probably shouldn't forget about dosbox.

Other search terms related to doom and their ratings are:
★★★★★ dosbox
★★ rockbox
downward
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Google Trends

Scale is based on the average worldwide traffic of doom in all years. Click on graph for more.
doom
quake
iron man