Tell us what your greatest gaming achievements are!
I haven't really done much.
Best thing I've done is play through Castlevania Symphony of the Night without dieing or saving...
I lost my memory card, and hadn't played the game in a long time, and wanted to kick Dracula's ass...
I can't think of anything challenging right now... I'm not the kind of person who goes for Hard mode and such... But one thing I did do was play The Legend of Zelda: Majora's Mask for 12 hours straight. That's one of my achievements and, I think, my personal record.

Beat Halo 2 on legendary in 6 hours (no cinematics). This was achieved with my 1337 dodging skill.
Oh.. and ALOT of running away and AI exploit glitches...
First: Going for three (count 'em, three) months without losing a lightsaber duel on Jedi Knight II Multiplayer.
EDIT: Yes, I was playing steadily throughout that whole period.
Second: Beating Mega Man X in a grand total time of 55 minutes. (God, I have no life.)
Third: Destroying a Star Destroyer with only an X-Wing without dying. (From X-Wing vs. TIE Fighter.)
Beat Emerald Weapon on FF7 w/ OUT knights of the round.
All your chars were 7777hp or something

Personally... It'd be beating Metroid Prime 2 without dying once, on my first time playing. Most people will get pwned @ Boost Guardian xD. I ended the battle with about 50hp (which is rather awsome). Didn't try it at hard yet, though.
Sorry can't think of anything else

My greatest gaming Achievement is the first time I played CS (counter-strike) online, I joined a public game and got top rank in the server in under 20 minutes (it was a new server but still, it was my first time playing lol) but then I joined another server and got wooped damn awps only

Halo PC Demo:
-Getting flung through a cliff wall accidently
-Insane Warthog Jumps
Einhander:
-Actually beating it
-Getting all the secret weapons
Robo Pit:
-Beating it. Every time.
G-Darius:
-Getting to final boss without dieing once/twice (I forgot)
Counter-Strike:
-Just because I felt like saying it, going Duel Beratta crazy
Unreal Tournament:
-Having so many mods/new gametypes/mutators that the 'Create Game' screen thingy lagged so much before actually opening up
Unreal Tournament 2004:
-WICKED SICK!!
Heh, I almost beat Einhander. That was an awesome game.
One thing I remembered was that I beat all the bosses in Mega Man X3 using only the X Buster.
beat doom3 without dying.
beh I can't remember my other great achievements
My greatest gaming achivement... hmmm... That was getting the scirpion (the tank) onto the
platform above the flag on the timberland map in halo 1.

The greatest game achievement I have EVER done was beat 3 games without saving...But of course I saved at the end of each game...I was extremely bored.
I have got a direct hit on my brother's chest with a tank shot from across Blood Gulch, with my friggin' LOW res TV.
Another thing, not really an achievement, per se, but an awesome moment...
I was hiding out in the Sidewinder base, while my brother was trying to fling grenades up into it to kill me.
Suddenly, I noticed some sparks, and realized he had hit my visor directly with a frag grenade out of pure blind luck. That saved me. The grenade, had it been a few pixels higher, probably would have went past my head and detonated behind me, without my noticing its presence...
EDIT: And not really an achievement, but still cool, I melee'd the shit out of Red Elites in Legendary Halo. It's fun. Too bad Halo2 Elites will kill 1 hit with Melee in Heroic/Legendary >_<