Go-Busters.
I've ragged on a few shows before that I didn't enjoy or were bad, but Go-Busters made me genuinely want to scream "What the f*ck are you thinking?".
It's not like it was a failed show in the sense that what they created with concepts, ala Turboranger, everything was picture perfect on paper; they just managed to screw it completely up consistently. Even with throwing in new characters and changing the show completely, they just couldn't get it to work. I mean come on, it's military Sentai show, the series has done this concept 10 times before and not managed to buggar it up.
'cept J, he was awesome. But did absolutely nothing the entire time.