Boy, I didn't think I could come up with 50, but I ended up having to whittle down my list (see: Honorable Mentions). I haven't really thought about how much videogames have been a part of my life, but they really have. And they still are, although in much smaller doses these days. In alphabetical order, because ranking is too much hassle:
Adventure - Did you know this contains the first ever Easter Egg? Of course you did.
Assassin's Creed II - I love the mechanics of this series, and wish I had time to play the newer ones (although all the stuff with the boats sounds dumb). The games tend to blur together in my memory, but I believe II introduces the thing with collecting artwork, which I thought was a great addition.
Batman: Arkham Asylum - I don't really give a shit about superheroes, especially not Batman, but this one had a very pleasant open-worldy collectathon-ish to it. Lots to do.
Brutal Legend - Yeah, you're gonna see a lot of Double Fine/Tim Schafer on my list.
Bully - The Rockstar formula in a boarding school? Yep, works like a charm.
Burnout 3: Takedown - Call this a vote for the whole series, but I feel like Takedown was the most satisfying.
Bust-a-Groove - One of the few game soundtracks in my music library. Insanely catchy tunes, fun characters, solid rhythm play.
Candy Crush Saga - Yeah, that's right. I can't call this a great game... but it sure is addictive. And generally pretty fun, as long you don't fall into the trap of buying extras. I've pledged not to do that, although maybe once a year I'll throw down a buck or two when it means I can pass a level I've been stuck on for weeks. I'm quite certain I've put more hours into this than any other game. By a large margin. Currently on level 3942.
Civilization II - I loved the first one, but the second is when I really got hooked. I was never great at it (I remember being SHOCKED at how quickly my opponent grew his civ in my first online game) but it's the ultimate "one more turn..." game.
Costume Quest - Oh look, it's Double Fine again. This game and its sequel are both delightful.
Crazy Taxi - You have to be willing to let The Offspring and Bad Religion into your ears, but besides that, what a load of fun.
Curse of Monkey Island - I know the first two games are more revered, but this is the one that's stuck with me.
Diablo - This game ruined the first real relationship I ever had. It was a doomed relationship anyway, but my Diablo addiction was definitely a factor in hastening its demise. Loved the second game too... I'd love to play III, but I just haven't had the time.
EverQuest - Oh dear oh dear. Diablo was bad, but EQ utterly consumed my life. I lived and breathed EverQuest for about an entire year. That world is as vivid in my mind as the neighborhood I grew up in. I'd stay up all night playing and call in sick to work the next day. And when I did go to work, I'd spend most of my day on EQ websites. Really, the ugliness of my EQ addiction was responsible for me realizing I needed to make some big changes in my life, leading me to quit my job in data entry and pursue a career as a programmer. And I made well over $1000 selling my EQ character and possessions on eBay.
Fable - To be honest, I don't remember a lot about this except that I really enjoyed it.
Final Fantasy IX - Sure, VII was great, as were the ones before that, but IX is the one that really sucked me in. I recall that the ending choked me up.
Flower - Can I count this as a vote for Journey too? Both are sublime experiences... Journey perhaps more poetic but Flower a bit more "fun" to me.
Grim Fandango - I long considered this my favorite game of all time. I played the remastered version and it still holds up. Not sure I would call it my favorite (a bit too much repetitive running around) but the characters, music, design, writing and puzzles are all of superb quality.
GTA: San Andreas - I never did get to play V (and let's face it, probably never will) and I have some reservations now about the excessive violence and misogyny, but Rockstar knows how to do an open world game. As evidenced by the preponderance of Rockstar open world games on this list.
Heroes of Might and Magic II - I also loved I and III, but I believe II was the one I played the most. I really miss this series, and I should probably seek out some newer turn-based strategy games.
Hot Shots Golf - Y'all can take your hyper-realistic golf games and cram 'em. This cartoony version is addictive in its simplicity.
Impossible Mission - "Stay a while... stay forever!!!!" is permanently etched in my brain. Devilishly frustrating (and hard to understand without a manual) but always a fun challenge.
Inside - Creepy, haunting and just the right level of challenging. One of most insane crescendos to any game I can think of.
Jade Empire - I do love me an action RPG, and this one includes respectful, tasteful use of Chinese mythology to build an engaging world.
Jet Set (Grind) Radio - SO MUCH FUN. I would play this again in a heartbeat. What a unique premise, and loaded with style. Can we have another?
Jumpman - Just a lot of fond memories playing this with my buddy, which led to the strangest in-joke we have: "The Bruce Boxleitner Screen" (don't ask how or why that happened, because I don't remember)
Katamari Damacy - Pure nuttiness, and an amazingly catchy soundtrack.
L.A. Noire - Open-world game with a film noir theme? Was Rockstar reading my diary?
Lara Croft and the Guardian of Light/Lara Croft and the Temple of Osiris - Yeah, I'm bundling these together because who cares. They're basically the same game. Great co-op gameplay made these a fun time for the wife and me. Can we have another?
The Longest Journey - Stunning adventure game with a rich story and well-developed central character. The sequel (Dreamfall) was enjoyable too, but not quite as good.
Monster Rancher 1-4 - The perfect games for someone with a huge CD collection. What would the modern equivalent be? Generate a monster based on a Spotify playlist? Whatever form it would take, I would love for this series to come back.
Okami - Beautiful artwork but also engaging gameplay.
Overcooked - Playing this game with a loved one will likely test your relationship. We have had fights over this game (and its sequel) but in the end it always leads to better communication. Sometimes very frustrating but always satisfying to beat a tough level.
PaRappa the Rapper - Kick, punch, it's all in the mind! Cute and charming. I miss this simple style of rhythm gaming, but what really set PaRappa (and its sequels) apart was the incredibly unique style and delightful sense of humor.
Portal/Portal 2 - Another wonderful co-op experience. Outstanding puzzles, wry sense of humor, intriguing world.
Rayman Legends - Once again, it's the co-op play that lands this on my list. And once again... can we have more, please?
Red Dead Redemption - While I think it's a little premature to be calling the sequel THE BEST GAME OF ALL TIME, I understand getting swept up in the moment and the hype. And I'll admit it, I'm jealous. Because the first game was truly a sublime experience, incredibly immersive with so much to do.
Resident Evil 4 - The best of an excellent series.
Saints Row - GTA with a sense of absurdity. The games get progressively more insane and to be honest I couldn't tell you which is my favorite. They're all a lot of ridiculous fun.
Shadow of the Colossus - Gorgeous and quietly melancholy.
Shenmue - Who knew driving a forklift and using vending machines could be so much fun? The sequel was excellent as well. Will somehow have to find time to play III.
Silent Hill 2 - I'm a fan of the whole series (and will defend the movie, though not the second one), but yeah I guess this is the best of them. So much atmosphere, and legitimately terrifying at times.
Space Channel 5 - I tell ya, I'm just a sucker for the old school rhythm games. One of those titles that made Dreamcast such a special console.
Stacking - Double Fine strikes again. What a weird and unique idea for a game, and the puzzles are terrific.
Telengard - This is an obscure, cheapo dungeon crawler for the Commodore 64. There's nothing special about it. It's on here because it was the first and only time I ever "hacked" a game. After reading a lot of Compute!s Gazette I realized I could just edit the source code and easily figured out how to give my character maxed-out stats. Which, of course, instantly made the game completely boring. But it was a proud moment.
Tomb Raider - I guess the first one, for nostalgic reasons, but I enjoy the series as a whole. Except when it's more about shooting enemies than exploring and solving puzzles. Still need to play the latest.
Tony Hawk Pro Skater - This was especially meaningful to me because a lot of my friends at the time had been into skateboarding. We spent many hours mastering perfect runs. Dead Kennedys on the soundtrack was very cool as well.
Uncharted - The whole series (although 4 is still sitting on my PS4, waiting to be played). Great characters, absorbing gameplay. I mainly play for the single-player campaign, but this is one of the few games where I'll do some online deathmatching.
Worms Armageddon - So many satisfying ways to stick it to your opponent.
You Don't Know Jack/Jackbox Party Packs - Cheating big time on this last one, but all these are great. Yes, there are a few duds in the Party Packs, but for the most part these are always a hit when friends are over. YDKJ stands head and shoulders above other trivia games thanks to its humor and sideways approach to questions.
Honorable mentions: Darkstone, Fatal Frame series, Crash Team Racing, Archon, Marble Madness, Racing Destruction Set, Viewtiful Joe, Pitfall, Elite Beat Agents, Warioware, James Pond 2: Robocod, Joust, Realms of Impossibility, Karateka, Broken Age, Psychonauts, Dangerous Golf, Combat, Bard's Tale, Ultima IV, Burgertime, Hydro Thunder, Power Stone, Brave Fencer Musashi, Samba de Amigo, Lemmings, Temple of Apshai/Gateway to Apshai, Ghettoblaster