Firstly: Seriously people, Mass Effect? Mass Effect 2 I could sympathise with, but Mass Effect 1 had like 5 above-average tracks (and admittedly 2 awesome ones - Sovereign's Theme and the end-credits song). Also, I saw some people nominate Half Life - and my irrational scepticism towards that game series prompts me to ask "link plz".
Anyway, onto my offerings.
Offering 1: the Halo series
I've never seen anyone criticise the music in the Halo series before (other than one troll on youtube, but hey, if he seriously believed what he said...)
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This is one of the coolest soundtracks I've heard in a while. Same goes for this:
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The choral section at the end is very beautiful.
Finally, there's a piece in Reach which contains a whole collection of excellent classics from the series remixed.
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Offering 2: Mass Effect 2
The music in ME2 is mostly just "above average", but a couple of my favourite pieces belong in here:
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Offering 3 (you really should have seen this coming): Homeworld
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Listen to this piece. Just listen to it. Tune out all other noises and immerse yourself in it. You get a prize if you tell me, utterly truthfully, that this isn't a beautiful piece of atmospheric background music that really gets across the vast, unnerving emptiness between the stars.
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This is very good battle music. It's catchy, but far from generic - it's actually very different to most battle tracks. Hell, those vocals (I think they're vocals...) sound almost haunting after a while.
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This is also very good battle music. It sounds subtly deadly and ominous at first, but then becomes a disturbing tribal motif. It's one of my favourite pieces of music ever - if not my absolute favourite.
So, there we have my favourite soundtracks ever. Don't ignore them, many though they are. Your day will be better for listening to them.