Al is the philosopher's stone. Also, "our" world is what's across the gate, and every time someone uses alchemy someone here dies. Ed and Al's dad is over here (thus not over there). Ed brings Al back as a kid (IE: before all this) and Al has no memory of what happened.
Oops..sorry. ***spoilers***
But yes, Cartoon Network has shown a LOT of better anime (though FMA is still good). And yes, next to Bleach and Naruto FMA isn't that great. And next to uncut One Piece (it's actually good uncut!) even Naruto pales.