Have to go with Galaxy. While I love Metroid Prime and RE4, it took until they got Wiimote pointer controls for them to really click with me. Going by pure impact on the industry it's neck and neck between Halo and RE4, as each defined what console first person and third-person shooters became, respectively. But RE4 is far and away the better game of the 2 in my opinion since even with keyboard and mouse controls Halo 3 was the only game in the franchise that I felt was truly great and even that isn't one of my favorite games ever. If this was 2010 I'd have gone with Twilight Princess, but since Skyward Sword and Breath of the Wild I've found TP to have aged somewhat. It's still great, but no longer my favorite game of all time. Galaxy, meanwhile, is just as amazing as ever.