Ultimecia from FF8... they spent forever developing Edea and a fair while on Adel, but all we got for the arch villain was a couple of cutscenes and a threadbare explanation of her evil plans. Compared to other Final Fantasy villains like Kuja or Sephiroth, there was nothing!
Same goes for Weiss in Dirge of Cerberus - next to no development.
And also, I have a bone to pick with Kingdom Hearts 2. Introducing a whole bunch of new characters in Chain of Memories!?! Some of us PS2 users don't HAVE a GBA, nor can we AFFORD one. A lot of it just made no sense... I had to rely on wikipedia to fill in the gaps for me.
And they did the same thing with "Final Fantasy 7: Before Crisis" and "Crisis Core"... My mobile phone is a Nokia 3310, so I can't play mobile games. And there's no WAY I could afford a PSP. This seems to be a trend Squaresoft are developing... if you want to follow their games, one console is not enough. I find it very annoying.
Anyway, technically these various new characters aren't poorly developed... but the choice to spread them across multiple formats means that many people have no idea who they are or what's going on.