I bought my 360 in April of 06 and the first achievement I got was for Perfect Dark Zero for beating the game on Agent difficult. ( I only got 10 points wtf.......  

Whatever the easiest Hexic HD one is.

Off The Boat in GTAIV. 
 
My first trophy was for collecting a treasure in Uncharted: Drakes Fortune.

" Whatever the easiest Hexic HD one is. "

whatever the first one on project gotham 2 was or was PGR3 the launch title? man i can't remember.

My first achievement was the first one you get in CoD3, it came with my console. 
 
My first trophy... something in inFamous? I think? I don't really care about trophies so I don't know. I WOULD have a lot more trophies if all the games supported it...

Escaped the Imperial Sewers from The Elder Scrolls IV: Oblivion

" Escaped the Imperial Sewers from The Elder Scrolls IV: Oblivion "

First trophy I got was something from Uncharted, probably related to getting headshots or shooting X number of dudes with a certain type of gun. 
 
You know what they say, the first time is seldom great.

Something in Advanced Warfighter, Gears of War or Call of Duty 3. Those were the game I bought with my 360.

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

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" @Vod_Crack said:

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

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I don't know... Something in Halo 3; probably Fear The Pink Mist ..

Brought an Xbox.  
Bleep bloop. 
 
There was confetti. It was beautiful.

Toaster in the Tub in Bioshock, I think.  I wasn't on live at the time, so no timestamp.

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

"

" @Vod_Crack said:

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

"

"

November 22, 2005 
Kameo - Found Pummel Weed - 20G

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

"

The one where you break out of Abstergo in Assassin's Creed 2. I only got my 360 last Christmas. 

Either "Prison Break" or the active reload achievement from Gears

The first achievement you get in Assassins Creed, I was late to get a 360 because the PC was happening. 

Gears Of War - completing Prison Breakout.

Freefall-Dead rising.

When I bought my 360, my friend also bought the first Lost Planet. we put that in my console and he beat the first level and we got that achievement.

I played for a while on my little brother's profile, so I don't know :(

Man, it has to be either Perfect Dark Zero or King Kong. But since Perfect Dark Zero was the first game I remember buying, I'm guessing it must be that.

I want to say May 2007 in NHL 07....simpler times.

Gears of War - Prison Breakout: Complete the tutorial level on any difficulty.

Some stupid Saint's Row achievement

whatever the first one you get on Gun is.

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

"

" @Vod_Crack said:

" @zombie2011 said:

" Whatever the easiest Hexic HD one is. "

"

"

Escaping the Imperial Sewers in Oblivion. I was so stoked, but that game sort of fell flat for me after that. 
 
My first Trophy was probably something from inFamous.

Forgot which one but it was from Condemned the day the 360 was released. I is OG, yo.

" @RockmanBionics: yes but were talking about xbox.........    I deleted Hexic when I first got the system so now I will never play it "

 The "Prison Breakout" achievement in Gears of War (1/15/2007).

""Prison Breakout" for Gears of War. 10 points for beating the tutorial on any difficulty. What a happy day that was. "

Ten headshot kills in Perfect Dark Zero, man that game was terrible at giving out achievements.

 Achieve 40 Consecutive Rallies in Virtua Tennis 3.  
 
Seems pretty random :P 

Marvel Ultimate Alliance - I Have a Friend
 
MUA came with my 360, along with Forza 2, so yeah. Beat the first level with my brother.

" "Prison Breakout" for Gears of War. 10 points for beating the tutorial on any difficulty. What a happy day that was. "

Got 360 a little over a year after launch. 
 
Call of Duty 3: 
Basic Training

Completed the rigors of basic training.