Does Tetris count? Pretty sure that game is the hardest.
In terms of games that are actually beatable, I found Dance Dance Revolution (I know...) outrageously difficult on the harder settings, although it is arguable what "beating" DDR is.
The toughest game I have actually beaten is probably Metroid Prime 2: Echoes. The Boost and Spider Guardians are tough as hell on Hard mode, and Emperor Ing is no walk in the park either. Halo:CE on Legendary was also outrageously difficult, although if you just keep playing from CheckPoints its not that hard to beat. However, Halo 1 on Legendary without dying is...something that exceeds my skill.
Playing DDR on any "difficult" setting really depends on how you play it. There is either the arcade version where you play with of course your legs; the PS2, etc., console versions where you play with the controller (which is easier), and it all depends on what song, and that if you don't play on Heavy mode, Oni mode, or higher, than it's not difficult. Some songs are just near impossible to complete on Heavy, therefore they become a nice Standard played song.
As for it being difficult on home systems, I'd have to say using a Xbox/360 controller playing DDR games with the shitty D-pad is very frustrating; this is why I prefer to play it either on the machine itself or on my PS2 (and I dislike the stupid gamepads they come with -- those things are shit, unless they have a metal one with one of those handle bars that come with it like on the real machines, then okay, cool).
Halo 1 on Legendary was difficult, but there were ways to get past it back then. Playing Halo: Reach on Legendary has made me realize how easy it is on Halo: CE on Legendary. Though, the only time I beat Halo: CE on Legendary was with my brother and the hardest part to get past was where all the convenant are in the cafeteria/kitchen area, and they are hard as hell to kill because they are grenade happy and their shots kill you fast. How'd we get past it? Every time we'd run out of pistol ammo (the assault rifle sucked, admit it, and the pistol in Halo 1 was godly) one of us would rush into the cafeteria with our grenades and use the assault rifle until we died... which was quick due to the damage done to you on Legendary mode. So, every time one of us did that, and we needed ammo, we'd just hit one or the other in the back which instantly kills you and then you can respawn and do it again, etc., etc until all the convenant was removed from that area. As long as the other player is alive, you don't have to restart from your last checkpoint, which was nice.
Figured someone would mention this once I clicked on the thread. I don't recall ever beating that game. Also, has anyone mentioned Superman 64? Or the old Mortal Kombat games? I remember I use to suck at MK Trilogy as a kid when I played it on my N64, so I turned the difficulty to the highest level and would pick the ladder with the most characters to fight against and I'd let them just kick my ass and if I was lucky, they'd do a fatality on me. Since I didn't know or could do a fatality or anything else on a N64 controller with those button combination's, I'd just watch the CPU slaughter me and put a smile on my face to see a fatality or something cool happen as I saw my character go to hell... or er, Netherrealm? Also, anyone remember the Mortal Kombat Mythologies game where you played as Sub-Zero? That game wasn't
that difficult, but it was very frustrating.
~ Aether Nexus