This can't be a poll, there's waaaaay too many possible choices and the poll will skew things. Something in the poll though that's important that a lot of people miss is that this says, "What's the most revolutionary game for you personally that broadened your mind," or whatever. It's not "what game changed gaming the most," in which I'd agree, Mario 64 was the first best example of the 3D platformer and made the template for a generation of 3D platformers after it. Mario 64 is like GTAIII in that way in that after Mario 64 came out, suddenly the industry was awash of clones or other games trying to do the 3D thing, just like how after GTAIII every game was trying to be GTA with the 'open world' mechanics and mission based structure.
But to the actual question....
I'd like to say Half-Life for me personally, but it's hard to pin that squarely in the 90s. I got Half-Life going into the spring/summer of 1999 for my birthday, and so the decade was basically over by then. Half-Life turned me into a PC gamer squarely, it's what made me build new PCs, I got super into modding and development, into running competitive servers of Counter-Strike and TFC, it's the first game I *really* got into multiplayer online gaming. I had done it a bit on LAN with Doom or Quake, but Half-Life and the mod scene is what turned me into a competitive online gamer.
But for me most of that happened in 1999 and beyond, so it's tough for me to really anwer. Still, HL came out in the 1990s, even if it didn't affect me as much until 1999 and beyond, it's still a "90s game," so that's my answer.
But... excluding Half-Life... I want to think about it. Doom was big for me, it was my first first person shooter. Mortal Kombat as my first fighting game.
For me, though, it's one that isn't on the list -- Madden '96. I had been into sports games as far back as the NES with "Golf" (now probably known as "MArio Golf," but it was just "Golf" then), Baseball, Double Dribble, etc. On Genesis, I was into Jordan v. Bird, Celtics v. Lakers and the NBA Playoffs, the Joe MOntana series / Sega NFL series, and more. I was really into NBA Live '95 and '96, but Madden '96 was the first sports game that I really got into sports simulation... Like, the idea building a team, running plays, scheming, not just finding money plays and trying to glitch the CPU or my friends with money players/teams/plays. What's funny for me is I got Madden 96 for Christmas from my parents, after I had asked for NFL '96 Starring Deion Sanders, the Sega sports football game, and I thought MAdden was *so hard* and *so boring* when I first played it, it was frustrating for me, the money plays that all worked in NFL '95 didn't work in Madden (NFL 95/96 was a horrible game, but I didn't know this at the time). My parents asked the guy at the counter what the best football game was, and he said Madden (he was right), but I hated Madden at first ..... until it clicked with me, and then I just realized how much better it was.
If there's one series I've sunk more time into than any it's Madden and NCAA Football. Even still, 25 years later, while I am super frustrated with the direction of Madden and sports games today, Madden '96 was the game that got me serious about sim sports games. I ran sports gaming websites, got tickets to E3 because of my sports game coverage, flew to EA events back in the day. So, yeah, I'm going Madden '96 in the poll, a game that will get 0 votes from anybody else, but probably the most important game for me.
