My Gamerscore is exactly 24757 and i am quite proud as i have got this from just playing games, apart form the fact that i have played 113 games, and i got my xbox on chriatmas day 2007.
My hardest achievement was either completing RE5 on Professional (War Hero), Completing Dark Sector on Brutal (Dark Sector - Brutal), and Completing Mass Effect on Insane (Medal of Valor)
My Proudest achievements are "Welcome to the Animus" (because it was my first) and "Blade in the Crowd" from Assassin's Creed. And any achievement i got on Fable 2
My most memorable was when i was playing Mercenaries 2:World in Flames, and all of a sudden the game stopped, and crashed and before i could switch it off, it came back on, only there was a message popped up saying 13 Achievements for 470G, when i looked at my achievements, I had unlocked all the achievements i was missing, even the ones that require online play and i didnt even have gold at the time. Kinda took all the fun out of it