Playing through FEAR, and the expansion packs on the hardest difficulty, both long, and hard (not to mention freakin scary).

Longest time playing a game would be Mario Kart 64 followed by Oblivion. My friends and I spent an obscene amount of time on Mario Kart 64.

Hardest, I would say 7th Saga. Been too long since I've played it, I don't remember why. But It's stuck in my mind as the hardest game I've played.

hardest: batletoads

longest: dragon quest VII, my brother first erase my save data when i was 60 hrs into the game, then when i start playing again he sit in the memory card and ruin my game of 50 hrs. and for the last time, when i finally finish the game, i spend 90 hrs, so in total it toke me more than 200 hrs, thanks to my brother, to finish the game.

Hardest would be DoR, longest would be Phantom Hourglass.

Hardest: Battletoads, I have never been able to beat it. Contra is a close second.
Longest: I've played Super Smash Brothers Melee more than any other game, but longest in a single-player game would be Final Fantasy VI.

Hardest and longest game I've played is "I Wanna be the Guy" if you dont know what I'm talking about search for it on youtube. Hardest. Game. Ever.

Longest: The Tick for Snes. The game is 5 hours long and there is no save feature.

The longest game I've played is easily Travian, both in playtime and real world time. One year of gaming pretty much every single day (apart from a few weeks of holidays). I don't dare count the hours I put in it, but it must be close to 1000 hours if not more.

Hardest game is more difficult to say, but perhaps 4D Sports Boxing comes close. I could never get past 10th rank. My friend who was almost a pro in it managed to beat the champ by points, and by not going the full 12 rounds. Otherwise I think it's nigh impossible to beat the champ.

Yeah well I didn't count WoW.

 Because yeah, it's gonna be hard to beat my 200 or so played days.....

Most games are long and hard for me...because I suck at most games.