(other than the quality of animation...that's a moot point).
Just out of curiosity, were you suggesting here that Seed's animation was of high quality?
From reading this thread, I think I'm something of a rare breed - I like the older stuff, from UC and Wing all the way through to Seed. Destiny was poor in parts, but even it had its moments.
What I'm trying to say about Seed's animation is that many people seem to fall back on saying that the animation was really good. Controversially, I disagree. Seed's animation was high-def, digitally coloured and pin-sharp - but I thought it really lacking in soul, and grit. It's hard to define, but I find many visual elements of Seed quite soul-less, including the character design (there's an image floating around 4chan showing how similar all the characters actually look when you change their hairstyles).
In your post, and others in this thread, people have mentioned preferring the characters of certain series, and I think the problem with that is there is a danger of accruing too much of a character's "character" to the writing. The characters in each series are realised through a mix of the writing, design and animation; this is part of the science of animation (and it's the secret to the success of, for example, Wallace and Gromit, because all three elements work in unison in Aardman's work).
If you like Seed, and feel for the characters (note: FEEL for them, not merely LIKE them - obviously there's a difference), if you haven't seen it, watch Gundam 0080: War in the Pocket. That OVA is almost entirely about the characters, with sporadic mobile suit battles. It's about many things, but one of the main themes in it is that many Gundam fans would love to actually live in the Gundam Metaverse - well 0080 is about a normal boy who does, and loves it - at first - but then through various experiences is made to realise that evil comes in all shapes and sizes and is forced to accept the true horrors of war.
I don't want to knock Seed, because I sat through it and enjoyed it enough - but I will say that I remember very few specific moments of it, whereas the original Mobile Suit Gundam, or 08th MS Team, or 0083 throw up a lot more memories for me. I don't know if that's much of a review.
Certainly if you like animation, do watch 0083: Stardust Memories, especially if you're someone who has grown up more recently with Naruto and Gundam Seed. Watch an anime that typifies what things were like before digital colouring, when anime was still gritty and dirty. You might be thinking even now "well I've seen Death Note" but believe me, it was different.