Mega Man 2 Pretty much any LucasArts adventure game (Day of the Tentacle, Sam & Max, Full Throttle) UT2k4 Doom 3 Prey (original) Dota 2
Company of Heroes with various mods - Eastern Front, Battle of Crete, The Great War and Far East War (if it would work correctly...) Have also recently gone back to Warhammer Dawn of War but with the Apocalypse mod. Call of Juarez Gunslinger
Civilization series (Civ V & IV) C&C series (RA1-2,TSun,C&C3+Kane Wrath) Witcher 3 Mafia 1&2 ETS2 & ATS GTA series(SA,IV,V) Warhammer 40k I&II NFS series(before Carbon) Warcraft 3 Starcraft 1&2 D2LOD Half-Life series (for mindless fun Serious Sam series) and so on.Oldies,but goldies.because todays game sucks.
Last year it was GTA V, Civ V and Football Manager 2017. No Man's Sky after each big update. At the moment it's FIFA 18 FUT but it keeps crashing (causing me to lose coins and points) so I have a love-hate relationship with it right now LOL.
Upon looking back... I can expand my list. Blood is my all time, absolute, without question favorite... but... there are other games I have installed at all times. And play periodically all year round. Hexen: Beyond Heretic System Shock 2 Quake 2
Football Manager! Every year i buy the new edition and normally i play it more than 1500 hours every game!!!... But latelly i´ve been playing PES18.
If a game cant provide any sort of variation to standard scripted gameplay, might be hard to consider it a 'go to' game. RTS games do a good job of providing enough variance as you're always curious to try out new strategies. RPG games maybe next since new characters, abilities draw you in for another go. Otherwise, scripted games with little variance can get monotonous for me on second go.
Half-Life 2 SP or MP - it's one of the few MP games I've always enjoyed immensely. Thank you gravity gun, ripping a urinal off the wall and killing an enemy. UT99, UT2K3, UT2K4 series died after these. I still can pick any of these 3 up for different reasons and play them for hours. I miss this series a ton. Thus a few rants on here about the UT4 piss poor beta.
I remember I got a crush on ladies (iron maidens) with rocket launcher. They made so sexy exclamation...
Until a month or two ago it would have been GTA5 but it seems that Rcokstar have no idea what direction, tone or theme they want for that game and are now just adding masses of expensive meme mobiles. Factorio and Rimworld are games I constantly return to mostly due to them still being EA it means that all sorts of new stuff will have been added since I last played the game, I'll then spend weeks playing them.
I suppose its skyrim. It never really loses the apeal to me. Playing it at the moment, maxing out those sneak 1 arrow deaths.
UT2K4 S.T.A.L.K.E.R. SOC F.E.A.R. (original) Crysis (to a point) need to startup Skyrim again ***Overall favorite*** Original Star Trek (DOS) where K was for the Klingon ships, R was for Romulans, and B were the star bases. Estimating the angle for firing the phasers or photon torpedoes was the built in difficulty.
Btw, anyone played a Quake mode/addon called Malice? It was quite revolutionary inventing such things as: jumps (no jumps in Quake), hoverboard (to let you jump higher and land from higher heights), scubagear, personal submarine, parachute, reloading and weapons without auto-reload, enemies shooting before die, 3D cinematic scenes made on the game engine, no armour, no health beyond 100, fire extinguishers on the walls to use if caught by flamethrower, probes with remote control, and cool powerful pistol (with cool sound) capable to be the only weapon. https://en.wikipedia.org/wiki/Malice_(1997_video_game)