That's the point though... There's just enough info about your character to make you "know him" With that info he seems like another grunt with no background... But in reality, he has gone through alot...
Read spoiler if you are familar with the Marines campaign: (yes, i know you are Cerb

)
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he lost friends in a mission they weren't supposed to take and also got in more personal trouble with miss Dunya... He had to break out from jail, kill guards that had nothing to do with this whole mess, and he resues his whole team, wilst recovering useful information on a disc, but the person who requested it killed herself in order to never make all this happen again...
But, he's just there... in a few cutscenes you see some highlights of the story, but mostly these are just objective based, and nothing that really takes you into the character and the actual situation... It would be so much better to add more personality, and feel more like it's worth controling the character...
Anyways, first time i beat it, i didn't understand everything, i had to beat it twice... then again, i wasn't very good at english back then...
My favorite Campaign is still the Aliens... it feels sortof cliche, and maybe not very new, but it's cool because it's working, and the levels are great... (like when a squad was expecting me from a certain direction, and i approach them from the side through an air vent (which was secured by sentry guns)
Man, i still want a remake of this game...