What's the hardest game you 100%'d?

[genesisfalls]

The title says it all. For me, it's Viscera Cleanup Detail:Santa's Rampage.

[Chris Fifty-Two]

Probably FORCED. Had some stuff that took a lot of tries and practice.

[{λ²} Порша Пудзель]

Half-Life 2 Episode 1 I HATED the 1 free bullet

[M]

Incredipede

[MrMcSwifty]

I'm sure a lot of people will scoff at this, but Call of Duty Modern Warfare 2 for me.

The High Explosive mission in the hardest mode in Spec Ops for the 69 Stars achievement is still one of the most challenging things I've ever put myself through in a video game. I would guess probably 30-40% of my entire Spec Ops playtime in the game was trying to beat this level with a good buddy of mine.

[courage]

The Legend of Heroes: Trails in the Sky (FC) 80 hours. There are too many items to be collected. I'm afraid I'll never 100% it without a walkthrough.

[Tolo]

Considering I don't have many games at 100% to pick from, I would have to say Mad Max, it wasn't necessarily hard, but definietly a grind. Took me about 64 hours to 100%.

I am however 4 achievements away from 100% Dishonored, some of the achievements have been a real pain, and the remaining 4 that I got left, made me take a break from the game. Not sure when I will get back to it...

[ShikenNuggets]

I haven't done many, but so far I'd say Arkham Knight. Skyrim took longer, but aside from the long grind it's not particularly difficult.

[The Phantom Chicken of CS_Italy]

Borderlands and Borderlands 2... I'm currently grinding away at Borderlands: The Pre-Sequel. I may have it before the year is over. ^_^

[yao199]

Beating Binding of Isaac & getting platinum god was challenging

[TheGhostik]

shadow warrior (heroic mode - it was pain in the ass)

[Jill of Trades]

Droplitz and Beat Hazard. Surviving for a long time takes a toll on both mind and body X_X

[Reaper]

pretty sure the blue ribbon challenge from bioshock infinite is still the rarest achievement on steam. so that'd make infinite a super hard game to 100%

[Simmy]

Bioshock Infinite. I had no trouble with 99 percent of the achievements in that game but that blue ribbon challenge achievement was a bitch. It's without a doubt the most rage inducing achievement I have ever earned.

[Light]

Maybe Rising Storm/Red Orchestra 2 Multiplayer with horrible internet connection (10 100% of 25618 players)...

[Cowboy(UA)]

Call of Juarez - The Cartel , because only glitched achievements.