Campaign Complete: Heroic
Completed the Campaign on Heroic difficulty.

Gamerscore = 100   Acquired 16/10/2009

Shortly after completing the game on Normal I decided to tackle ODST on Heroic solo.  I found that playing the game on Heroic was a more challenging and therefore, in my opinion, more enjoyable than my normal play through.  While I searched high and low for all the audio logs I still would up being four short of the 30 that could be found in total.  I will get them all one of these days!  Next stop will be the Legendary difficulty, but I will not be tackling that alone, I will be saving that for some co-op action.  A side note on the above, I actually finished the campaign on the 17th, but because I had already finished a couple of the levels on Legendary, it binged the achievement a little early.

 
 
Laser Blaster
Got 10 Spartan Laser kills on ONI Alpha Site.

Gamerscore = 5   Acquired 16/10/2009

Achievement Spotlight – 46,000+ Gamerscore: While completing the campaign I also was able to surpass the 46,000 Gamerscore plateau.  With all the games I have yet to play this season I believe I have an outside chance of cracking 50K before the end of the year!  We will see what happens.

Bungie.net : Halo 3 ODST

SUPERGHOST's Haunted House of Xbox

 
Campaign Complete: Heroic
Completed the Campaign on Heroic difficulty.

Gamerscore = 100   Acquired 16/10/2009

Shortly after completing the game on Normal I decided to tackle ODST on Heroic solo.  I found that playing the game on Heroic was a more challenging and therefore, in my opinion, more enjoyable than my normal play through.  While I searched high and low for all the audio logs I still would up being four short of the 30 that could be found in total.  I will get them all one of these days!  Next stop will be the Legendary difficulty, but I will not be tackling that alone, I will be saving that for some co-op action.  A side note on the above, I actually finished the campaign on the 17th, but because I had already finished a couple of the levels on Legendary, it binged the achievement a little early.

 
 
Laser Blaster
Got 10 Spartan Laser kills on ONI Alpha Site.

Gamerscore = 5   Acquired 16/10/2009

Achievement Spotlight – 46,000+ Gamerscore: While completing the campaign I also was able to surpass the 46,000 Gamerscore plateau.  With all the games I have yet to play this season I believe I have an outside chance of cracking 50K before the end of the year!  We will see what happens.

Bungie.net : Halo 3 ODST

SUPERGHOST's Haunted House of Xbox

Congratulations! I've been playing on Heroic since Halo 2, this game may be the first one I try on Legendary.

I want to get back and play this game on Heroic and Legendary, but Modern Warfare 2 is going to take up ALL my time this month.

My friends played through ODST on Legendary the night it came out. Heroic by yourself sounds like a real challenge though.

I did Heroic solo on my first playthrough, as is the way it should be done. Then I went back and got my Legendary solo on. Man, I love Halo.

I'd love to say I'm proud of you but Bungie themselves have said that heroic is what you SHOULD be playing on if you have ever played a fps before.  So color me unimpressed for doing the norm.  Perhaps I'm a little jaded because I'm a fan of the series and feel you should play on the hardest difficulty (It's a very different experience).  
 
So what difficulty do most people play on?
 
Personally I always go through on heroic first and then legendary right after and usually just play heroic when I want to play the campaign later.  I do suggest trying easy with all the skulls on -- they can't kill you very quick so you can go guns ablazin' but with tilt, thunderstorm, and mythic on they don't go down very quick either.