I really haven't seen any other gundams. But gundam seed really got me into mech anime's. I love the chracters. they are full of realism. what got me thinking was, that there are really no bad guys and no good guys. U have to choose. And with the conflict between friends it makes it even harder to choose who you like better.
Kira is kind of like Shinji, from evangelion, in a way. He thinks the Gundam is some destructive weapon that is only meant to kill. WHile that is partly true. Both of them find out that the Gundam (or Eva) can be used to protect. I think that really builds up the tension. Also How Kira is so protective of his friends u can't help but feel sorry for him. My favorite chracter is Mu(i think that is how you spell it) Laflagha.
And it is true that the Jinns do look like the Zaku's from other gundams. Except they looked revamped. And I don't know if the other Gundams have Mobile Armors but I think they are cool.