It's a love-hate thing. A lot of people love SEED but hate the other series, and vice versa. I can't say why for sure, since I haven't seen SEED. But I think the original MSG, 0080, ∀ Gundam, etc are pretty great. ∀ Gundam because you need to look at the character map to type it out, and for the Yoko Kanno music [even though IMO it's her worst work] Also, I remember not liking 08th MS Team, but I can't remember why. It had some cool parts in it, but I vaguely remember some ridiculous love story at the end.
But yeah, you could talk for years about Gundam, I don't think many people realize how much Gundam shit there is. Seriously, holy fucking god.