[Kamen Rider Lucha]

Honestly, I've never seen a Sentai that I'd rate as completely unenjoyable. So this is a little hard.

I would say Magiranger, as it's the only series I've outright hated, so much that dropped it around episode 22. But to be fair, I'll play by Matrixbeast's rules and limit this to series I've watched in full.

I guess I'd have to say it's a draw between Maskman and Megaranger. I tend to enjoy "baseline" Sentai shows that are technically fine but ultimately super bland the least. Mask & Mega def fall into that category for me.

A Sentai can be outright bad for most of its run, but if it has stand-out elements or moments where you can tell the creators are trying something new or ambitious, I'll tend to give it more credit that the middle-of-the-road shows that don't try to do much new and whose characters are cardboard cutouts. That's why something like Ohranger, the majority of which is pretty awful, is more toward the middle of my faves list than the two above mentioned series, which may be technically better but are consistently "meh."