The longest game you've beaten start-to-finish in one sitting.

[The_root_of_all_evil]

You have to burn the rope.

 

[CJanders]

Chronicles of Riddick: Escape From Butcher Bay

 

[Sinspiration]

Dirge of Cerberus in one day.. I was horribly disappointed..

 

[Twilight_guy]

None... maybe Portal. Games last pretty long and sitting down for the hours necessary to beat it make me feel like a slacker.

You have to burn the rope.

^--Winner

 

[Taldeer]

I could never be bothered to do that as some sort of test, but I'll say I've finished Mass Effect 1, KOTOR and KOTOR2, Syberia and Vampire: The Masquerade - Bloodlines in pretty much one sitting...

 

[Frozen Donkey Wheel2]

God of War 3 on easy mode. I mean, OK, I stopped ONCE to eat dinner, but still. Took a good 9 hours total.

 

[onewheeled]

...Portal.

Yes, that's it. I'm that pathetic. Though I am pretty proud that it clocked in at under an hour, which is good for me.

 

[suitepee7]

well the longest for me was probably Resi5, completed it in one night with my friend on co-op split screen, took 13 hours i think ^^

 

[alimination602]

Mass Effect, Zelda Ocarina of Time and Banjo Kazooie (On different days).

After those my fingers became paralysed and i couldn't make a fist for a week.

 

[Bugerion]

You are empty took me 6 hours on my blind playthrough

 

[SimuLord]

For Discussion: All there in the topic title. Something short like Portal? Something absurd like getting a World of Warcraft character to max level from level 1?

Only ones I can think of are getting through the campaign of MW2 in one night. Didn't feel too long though because of that.

I think the one that qualifies best is a tie between going through Ace Combat Zero 3 times in a row, nonstop, on the third to last, second to last, and hardest difficulty, respectively. It would be tied with probably an Armenian campaign in RTW that I finished in one day (nearly the full 24 hours). I had breaks here and there but I never quit the game so I consider that one sitting.

Funny you should mention Rome, because earlier this month I completed a full Julii campaign in one shot---Steam says 18 hours, but I'm thinking it didn't credit me with all of the time because my clock said 25.

 

[DenSomKastade]

Need for speed: carbon.
That game was very easy too finish the quick way

 

[Novania]

I did Halo 1, 2, 3, and ODST on legendary in one weekend with my friend on his xbox so we were going at it practically non-stop with quick breaks between games

 

[Bagmanith]

Portal and both the Modern Warfare games I completed in one sitting. Also completed the the first Mass Effect with completionist achievement in one weekend, alas not one sitting though. Damn you exhaustion.

Edit: After careful consideration I would like to add Blue Shift, Half-Life 1 and Doom 3 to this tally.

 

[Aiden_the-Joker1]

Ocarina of time. I had completed it before and knew everything. So one morning at 6am I started it and finished around 1 am.

 

[inkheart_artist]

Mega Man X when I was a kid.

 

[Mistermixmaster]

Heavy Rain is a contender for this one, but it is beaten by Metal Gear Solid 4. I played MGS4 in one sitting, watching ALL the cutscenes/briefings. That was epic as hell. ^_^

 

[Candidus]

A thirty-something hour playthrough of ME2 would be it. I almost finished Baldur's Gate 2 in a single session once, which lasted much longer than 30 hours, but I fell short after killing Bodhi.

I've done longer sleepless gaming stints, but on games like X:3 TC and MMOs, which are neverending and so fall outside the bounds of your question.

 

[FightThePower]

Sonic 3 and Knuckles. Didn't die once either.