I absolutely agree with you. I loved the first Super Mario Galaxy, and if you haven't played the first one, than you really should to get the gameplay down. Otherwise, you'll have a harsher time mastering the gameplay.
Storywise, it doesn't matter which one you play first. Both employ the "Peach is kidnapped by Bowser, go save her!" angle. Besides, no one plays a Super Mario game for the story.
The only reason to play the first game first is to gradually get you accustomed to the gameplay and challenge. The second game's difficulty picks up quickly, and starting on the first game makes that progression more gradual.
@ Zilla: Of course the first 20 minutes is easy. You really think you can judge SMG/2 by the first 20 minutes? Get back to me once you obtain all 240 stars with your death count (which the first one logs for you, anyway). Or if you can even reach them all.
The designers basically said this game was made assuming you played the first, so they don't generally "re-teach" you things (though there are a splattering of signposts and the instruction manual to do that) and difficulty starts around the place Galaxy 1 left off.
I would recommend Galaxy 1 first just to get a better feel for everything, but story-wise there isn't really anything to know. In fact, as far as I've seen, this game sort of ignores the story of Galaxy 1 and re-tells it in a different way.
Oh, and a note on difficulty - 1-up mushrooms are handed out like candy. I had like 40 lives by the 4th or 5th level I think. So while you may *die*, you likely won't get a Game Over.
@ Hawkeye: As someone who played the first Galaxy two years ago, I STRONGLY recommend playing that one first. Don't get caught up with the novelty of 2's release; it will still be there when you beat the first one. Just because the first one came out three years ago (oh, how time flies), doesn't mean it isn't worth your time or money. It's a phenomenal game.
Plus, by playing the first one before, you might appreciate 2 even more. I'm currently playing the first one again while my second one has yet to be delivered. I'm having a blast all over again!