One of my all time favorites would have to be ETQW
I don't know how many hours I've spent playing the same thing over and over again, but no matter what, It has always kept me entertained
As one of the first games I've ever played, it's pretty much one of my top favorite games ever

QuakeII graphics were not great, but the gameplay was fast and the weapons were fun to shoot.
Rockets, rail gun, flair gun, grenades, grappling hook...
I ran a server on my roadrunner cable for a few years. Did not take a lot of hardware to do it either.
Tons of fun.

samwasdroppingeaves
I don't know if I'll ever recapture the feeling I had when I first logged into WoW and just spent hours exploring with my friends. I've since left the game entirely but jeez it was a ton of fun and for that will probably always hold a special place for me as my favorite.

I started playing WoW with friends not long after launch and it was an awesome experience that took up way to many hours of my spare time. These days I'm strictly casual but have a semi-regular WoW session with my two oldest kids.

Probably blood borne. The lore is just fascinating

Its always been WoW as my answer, but both EFT and PoE are coming up on that. Video games are getting so dang good.

Outer Wilds. You asked why:
 
"The best game award of 2019 goes to: The Outer Wilds. There are so many games out there that feature space travel and yet none of them really gets it. The horror of an endless dark vacuum so intent on killing you that just 90 seconds in its inanimate presence is more than enough to freeze, suffocate, and explode you inside out. Space is literally the worst place in the universe. People always think of space as above us, but it's not really; you don't have to look up to see space, you have to look away from safety to see space. Then, when you're out there in the nothing, there are jewels; unprocessibly large balls of fire and light held together by our own ****ing anger, rocks that can range between husks of nothing or everything some life ever knows, and an endless amount of phenomena that would take our scientific knowledge and **** it from **** to breakfast. But video games just don't get it. They just don't get space. Video games set in space are either just men with big swinging dicks firing at bug-eyed monsters or ****ing truck driving simulators. If exploration does happen to be the focus, you'll find out that the main difference between the endless majesty that is life in this universe is the color of the ****ing grass. Yeah, you're in space but it feels inaccessible like a fingerprint wouldn't take on it; like it's behind glass. The Outer Wilds - ****ing hell - the Outer Wilds gets space. It doesn't care about scale or scientific accuracy, it gets the feel right. Yeah, your ship's made from wood and the majority of planets are the size of of a badly stocked Ikea, but watching all the stars in the sky go out one by one like far off fireworks and knowing that each one could be destroying an entire history and having to do that ****ing every 22 minutes -- nothing. Nothing has made me feel like that before. No game, no book, no movie. It's beyond extraordinary. Its planets - **** - its planets; each one a bizarre impossible place riddled with life and death and decay and nonsense. Each one dense in history and vandalized by time. Each one nightmarish and so, so beautiful and in 22 minutes, they're gone because the Outer Wilds isn't even really about space, it's about the question, the most important and terrifying and unanswerable question anyone ever asks: Why? Why bother? Why bother with any of this? People die, stars burn out, the universe will go quiet and dark and cold and in the longest run, nothing - absolutely nothing matters. Everything dies, the universe included. So why sit around the fire, playing music into a void that doesn't care? Why huddle around the light? Why play? Because, well - look at it. It's mad, all of it. Life is a big stupid blob of meaningless nothing. Yet from that, we find meaning. People, things, animals, art, sofas, cereal, Rubik's cubes, silly little games about space, whatever. None of it matters in the grand scheme - **** the grand scheme! There's no logical reason for life and nobody's gonna mourn it when it's gone, but that's what makes it fantastic. Life is a little song that we hum to ourselves and, I wouldn't want it other way. The Outer Wilds is an optimistic game about nihilism. It's a game with no invisible walls, you can complete it in ten minutes if you know what to do - which you won't for hours - and the only limit is knowledge. It's a game literally like no other. The universe is big and long and impossible and daft and you, you happen to be experiencing it at the exact same point that you can play the Outer Wilds as well. Embrace that coincidence. Come on, what are you waiting for? The sun could explode tomorrow." - Daniel Hardcastle 2019

racing and shooting games

Skyrim or Witcher 3
 
In both i spent countless of hours only to get all the vanilla things done. Modding was the key for even more. 10/10

Chrono Trigger. Absolutely blew my mind as a kid and got me into rpgs. 

Desktop Dungeons, try it if you like roguelikes.

Love hate relationship with ark. Played it more than any other game but hated it half of the time. Great game overall, awesome concept and as much as the devs piss me off, they provided me with hours of fun and good times with friends.

Halo 2 because I can't remember a game with a better multiplayer experience for me.

original vCoD - great campaign and the multiplayer was just phenomenal. There's a big nostalgia factor for me but I couldn't ever get enough of it. 

Gotta go with Overwatch or GTA 5 they're only games I've bought for multiple systems and played for years. Though the original pokemon and zelda OoT are definitely on the list too

Super Mario Galaxy. Best video game soundtrack with crazy good platforming and replayability. a must play for almost anyone.