Starcraft-I played Warcraft but the concept of Starcraft sounded corny to me so I had no interest. My mom took me and my brother to Best Buy and I got a Janes flight sim or something and my brother got Starcraft. It took maybe 2-3 hours of me watching him to know I needed it bad, I ended up getting it a week later. My brother had the Terran box, I got the Protoss box and that's what we both ended up playing mostly.
Tribes-I was heavy into FPS's at the time, but Tribes had gameplay elements so different from Quake that were a blast to play with like skiing, jetpacks, vehicles, different loudouts, etc. It's too bad the sequels have all been garbage. I only ended up getting the game because I thought it was a mech game hah. In the early days I remember playing with the lead programmer GotMilk or whatever, pretty neat.
Everquest-In that era pc gaming magazines were still big and the online articles were taking off. I would constantly read about EQ before it's release and the concept sounded amazing, but actually getting and playing the game blew me the hell away, but I don't have to explain all of those feelings to anyone here.
Dark Messiah of Might and Magic-There at a handful of games I won't mention here that were better games, but they were games I was expecting to kick ass. This game was a blast and you never really heard anyone mention it. The single player campaign was very interesting and hard to put down and the multiplayer, while very sparsely populated and not exactly balanced, was a blast.
League of Legends-I was a Dota player since 2003 and had no interest going into a new game, but after most of my friends migrated over I decided to try it out of boredom and the last 3 years it's been my most played game. The funny thing is Overwatch has pulled me away from it and it's the first FPS I have played a lot in years.