When I think of the hardest gaming achievements these spring to mind:
Astrosmash (Intellivision) - My peak score was somewhere around 800K-850K, since after 750K there is _always_ a guided missile on the screen and my hundreds of saved up lives drain away like water through a sieve. But somehow my dad could break 1.2 million, and did multiple times. He never even played anything else. I have no idea how that was even possible. At the time, I remember seeing a "world record" score in a game book of ~180K.

Here's an example of how crazy the game gets just when you get close to half a million,
http://www.youtube.com/watch?v=v07GKNN1FXc&NR=1 Note the beat change after the guy hits half a million, it's much MUCH worse after 750K.
Tron Deadly Discs (Intellivision) - Over 2 million points, at 1 million the enemies with discs get replaced by orange guards that end the game instantly if they touch you, so it's pretty tough.
Nethack - Been playing for a couple decades, and I actually ascended once a few years back!
Ninja Gaiden (NES) - Beat it without getting hit.
Jet Moto 2 - Won a championship season on Insane difficulty. The AI cheated like hell in this game on Insane, but I still managed to pull it off. This one nearly drove me insane with rage, so the difficulty setting was well named.
Tomb Raider (PSX) - Beat the game without dying or saving, with all secrets.
Tomb Raider 3 - There was an area where you could take one of two paths and there was a secret on each one, of which you were only supposed to get one. I figured out how to get both so I had one more secret than the supposed maximum total. :B
Earth Defense Force 2 - There are only a handful of missions I have yet to beat with both characters in Impossible difficulty. Never played co-op either, which would have made things eaiser, although I did use both characters at the same time for some levels.
Gran Turismo 4 - 100%. Beating the final Nurburgring mission was glorious.
N - Not N+, the original N. Beat every level. Mother Thumping Impossible took me the better part of a half year to complete.
Mirror's Edge - Platinum, 66 time trial stars. I think that's about the limit of what I'm capable of in the game.
Opiate said:
A perspective from a different type of gamer: I notice that everyone is posting single player achievements.
I am, for example, far more impressed by a 2200 chess rating as a game achievement than anything posted in this thread. Or professional starcraft players, or CS players, etc.
Not that everyone's achievements are stupid and bad or invalid: I'm just noticing that everyone immediately jumped to single player games.
Part of it is that the thread is about what achievements were hardest for you, and so the things that spring to mind are the bits you had to play and fail over and over before finally succeeding. In Warhawk, after nearly 8,000 games, I've got an overall 2.62 win/loss ratio and a >1.0 win/loss ratio in deathmatch. That's really good, but it's not something I think of when I think "hardest achievements", because I didn't struggle for that in the same way I struggled with the things in the above list.
I think if the thread had been titled, "What games are you really good at?" you'd be seeing a lot more mentions of online gaming.
As far my personal hardest of all? Probably nethack. After all, it did take me over a decade to win just once.
