Books and movies are often seen as conveying a message so why not games. Of course I don't actually believe that this is what most games try to accomplish but I think it would be a fun exercise anyway.

I'll start:

Every Mario Game Ever: Don't write off an ordinary mook from Brooklyn; you can do anything if you try.

Uncharted: Killing tons of people and stealing ancient treasure if okay, as long as you look good doing it.

LittleBigPlanet: Make your own fun.

God of War: Everything you hear about Ancient Greece is actually sugar coated.

Grand Theft Auto San Andreas: Just because you come from an impoverished ghetto neighborhood doesn't mean you can't go far in life. If nothing else at least you can swim.

Madden NFL 11: You bought Madden NFL 10 so you might as well buy this one too.

Your turn.

ha, I liked the God of War one!

Sadly, I'm not creative enough to make any interesting lines

Portal: your way to the exit 

Fix for you

Madworld : Add some color to your life

de Blob: You can never have enough color

Gears of War: See what life is like without it?

Demon's Souls:  "If you dont feel like breaking your controller (or crying) you are doing it wrong!"

Ar Tonelico 3:  "Dont you wish you could purge women's clothing this easily in real life?"

Eternal Sonata: "Proof that seeing music can be just as pleasing as listening to music"

Starcraft 2: "In the rear with the gear"

My favorite game:

FF10 - Religion is a joke.

Others:

Dynasty Warrors 3 - "Yeeeeeeahhhhhhhhahahh The children of the Yellow Turbans!"

FF8 - GF weed: makes you forget your horrible past.

FF9 - Monkeys are people too.

Demon's Souls - Not saying anything is just as awesome.

(Super) Street Fighter 4 - Cannon spike, Spiral arrow.

Kingdom Hearts - I love cheez-it.

Singstar - rah rah rah ah ah roma roma ma

LMAO

Describe a game in one sentence? Hmm...

GT5: "I was already six by the time I was born... 0_0"

Demons' Souls: "FYI, Umbasa doesn't give a shit about you, you cunt. Die."

Crysis 2: "I have the best graphics ever" -Slenor

Uncharted series: "The real Indiana Jones 4"

Katamari Demacy: *Head explodes*

FF13: "I'm not worthy of life"

Yakuza: every problem can be solved if you beat up the right people