Half-Life, STALKER, Quake, DooM and Elder Scrolls have not yet been surpassed. I won't write about races.
The series
TES
The Witcher
Dragon Age
Assassin's Creed only to Assassin's Creed IV Black Flag all the rest is slime.
Longest I've sat in:
The TES series
-SPORE
Second Gothic and the first Risen
-Dragon age origins
Many tighteners in my time passed, from among particularly long of course note:
Fallout 3 + new vegas, skyrim, prototype. Command and conquer generals, tiberium wars, GTA SA, GTA IV, Hitman Absolution, Crysis series (the first and second parts were replayed several times, in the first liked to indulge in physical mods). Warhammer 40k Dawn Of War (sat for about 500+ hours)
But in the top of the list is certainly Supreme Commander: Forget Alians, I have 1,783 hours in it at the moment. Too bad the multiplayer of this game is slowly dying because of the low online. I haven't seen a better RTS.
Well, from what I'm dragged into now, it's Metal Gear Solid V. 66 hours so far, the game is 40% completed, 35 story missions out of 50. I'll be coming back to this game for a very long time yet, not even a hint of "bored" yet.
Assassin's Creed since the first one back in 2008. To this day, all parts!
Assassin's Creed
Skyrim
WWW series and basically everything.
Fallout 2,New vegas.More I can't seem to remember.
I must have played 500 hours of skyrim, 250 - san andreas, 350 - warcraft 3(editor - our everything), stringhold cruiser - 150
The most addictive are definitely RPGs. The Witcher series, Fallout, The Elder Scrolls, Dragon Age.
I would like to mention Fable: The Lost Chapters and Star Wars: KOTOR 1/2, which I have passed more than once.