I thought the Undead was a pretty neat idea for a set of "villians". That group alone is what makes Blade one of my favorite series, the whole backstory with the battle royal and their reasons for taking part in it was great. It's always good to have an opposing set of characters with personalities as opposed to say the Worms from Kabuto in where all but like 7 only had any real personality (if you can call it that) and only 1 of them was actually around for a good amount of time.
Tachibana is...yeah, not my favorite character by a long stretch, at least in the early episodes. When his character starts to evolve and stuff, then he gets more interesting, but Hajime will always be my favorite of the Blade riders. His suit (and really all of the Blade suits) were sexy, I don't know how this series didn't have good toy sales.