If you can, see if you can just watch the cut scenes somehow. That'll catch you up on the story and buy and large being familiar with the story is the main reason to play GoW I & II before playing III.
If you're not too worried about being in the dark on some of the story elements then play III you can always go back to I & II if you fancy some more Kratos action. GoW III may be EPIC but I & II will always be games worthy of being played, because they were epic in their day.
Having said that, and having played I but only watched the cut scenes for II, I still plan to hunt down the GoW collection to play II before I buy III. But given I've played I already I don't really want to buy the collection at full price, so things are possibly a bit tricky for my plan coming together like I want it to.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
