Ohh this is tough one, not super duper tough one. I'd say Gears of War( or Gears) is the best IP in my experience because why not i liked ultra-violent action game with gruesome so much especially my favorite iconic weapon is Lancer AKA the chainsaw assault rifle-Chainsaw Bayonet.
Honorable mentions: Max Payne and WinBack(<psst this one is the old god of third of person shooter which in turn influenced games)