Not in any order, because orders are retarded.
1. Starcraft 1 and Brood War - Starcraft has and will always have a special place in my heart. I discovered it at a reasonably young age (10 or 11), and the experience of playing it, the story, the multiplayer, the graphics, sounds, cinematics, everything just came together and felt great. It was to me, the perfect game at the time. Also, it was a sci-fi game, and I've always been a huge sci-fi fanboy. I am pretty hyped about this new remake, so obviously I'm gonna play through the campaigns again and pick up multiplayer with my old friends.
2. Diablo 2 - I LOVED diablo 1, the ARPG genre always spoke to me, the grind, yet still somehow rewarding in and of itself. When Diablo 2 came out, and I remember being ectatic. I played THE SHIT out of it, and my entire time in high school basically consisted of playing D2 with friends, getting drunk, and going to a few exams n shit. The game was a perfect sequel, and it contained so much of what I love about the ARPG genre, and still does. MANY ARPGs have since come out, and some of them have been quite decent, but nothing holds a candle to the old formula that Diablo 2 brought. It basically became the go-to reference game, when making ARPGs.
3. Half-Life 1 - Boy, this was major. I remember being reasonably hyped about this game, reading about it in magazines (when people still did that LOL) and just loving when I read. When I finally played it, it really was a novel experience at the time. It had interesting designs, story, gameplay, and also the multiplayer was cool with ALOT Of mods that sprung out of it (CS and so on). It marked the beginning of an entire era of new games in that vein.
4. Command & Conquer 1 and Red Alert - Before Starcraft, the supreme king of rts was the C&C and red alert games. EVERYBODY played it, and everybody loved it. It was the grandfather of all the new rts' to come. It was so new and different, and had that basic formula down, that it was a blast to play through and kill your friends in multiplayer.
5. Quake 1, 2 and 3 - I've never been a huge FPS geek and multiplayer at that, but the first 3 quake games, especially the first ones, really blew me away. I've spent hours on end on these games, both in single and multiplayer, and it just was a perfect mix of a good fps game.
6. Heroes of Might and Magic 3 - The best of the series to date. Simply a perfect game from the genres standpoint, and it still plays fresh today. I remember putting hours into this game, and at LAN parties, people would play this and have a great time.
7. Resident Evil 1 and 2 - I've been a huge survival horror fan for years. And nothing beats the resident evil 1 and 2 games. I loved the RE1 remake, and I'm looking forward to the supposed RE2 remake, aswell. The games capture the essence of true survival game combined with horror elements and story. Really a thrill to play back in the day and still is.
8. DOTA 1 - I'm a pretty big MOBA fan, and I've played lots of dota 1 back in the day. Nowadays it's Heroes of the Storm, but nothing beat that experience of first playing dota 1. The MOBA genre has evolved alot since, but the basic formula is mostly the same.
9. Hearthstone - Simply a great card game, and a game I still play hours on end today.
10. Deus ex 1 - This game was simply great. I loved the sci-fi elements combined with a strong story. The gameplay was superb for its time and still is.
11. GTA 1, 2, 3, vice vity and so on... - What's not to love about the GTA series? From the first installments that were top-down, which I spent HOURS on in single and multiplayer, to the newer ones that evolve the genre. I played
12. Dark Age of Camelot - Simply the best MMORPG to ever exist. It had and still has the best PvP MMORPG experience ever created, the most complex and unique gameplay. Many have tried and failed to replicate the good PvP combat from DAOC. World of Warcraft was also good, but it was a wholly different experience alltogether.
13. Hitman series - Ever since Hitman 1, I've been an avid fan of the genre. Playing as a stealthy hitman is pretty damn cool. Excuting somebody and the slipping away unnoticed is wet dream come true. Great games, with blood money being the high point and also the new hitman 7 being pretty damn good. Absolution being the low point.
14. Vampire: Bloodlines - What's not to like about this game? It had a cool story, fleshed out characters, a cool unique rpg system and great writing. Its one of the codex' favourites and with good reason. Overall super good rpg.
15. STASIS, Monkey Island 1, 2 and 3, Day of the tentacle, full throttle, indiana jones and fate of atlantis, the dig, leisure suit larry series and so on... - I LOVE adventure games. I could make an exclusive top 20 adventure game alone, so I decided just to include most of the best in this one. There's countless others whom I won't mention, but can talk about in PMs with people. The ones mentioned here, are simply just great.
16. Theme Park and Theme Hospital - Great fun games that introduced me to simulators of all kinds. Park and hospital management was fun back then and still is.
17. Syndicate and Syndicate Wars - I. LOVE. THESE. GAMES. Simply put, syndicate and syndicate wars was the embodiment of everything I loved at that time. Great fast action, cool sci-fi story and elements, great gameplay and unique choices. It felt great running around with your specially thought-out agents and complete missions for weird and big corporations. The new game, sattelite reign, was a sadly big disappointment, however.
18. Jagged Alliance 2 - Super great turn-based game. It was one of the first games that really got me into tactical turn-based gaming.
19. Aliens vs Predator 1 + 2 + expansions - I love Alien and predator universes, and a game that combined all these things got me hyped. I played these games for hours on end in single and multiplayer and it is still great fun. Newer installments disappointed, and so did all the films, but these games were great.
20. Alien Isolation - A return to survival horror roots, and in the alien universe at that. Simply one of the best survival horror games to come out in the past decades. It was a thrill to play.