kyuranger has a very strong second half, and a very weak first half, is how i'd put it

Yep, while it still suffers from overfocusing on Red, at least you can tell the crew realized this and began focusing on other characters. It's when Tsurugi debuits the show became stronger, only cemented further by having Naga turning evil.

for Ultraman, I re-watched certain episodes of Tiga, Dyna and Gaia for nostalgia.

for Sentai, the only I rewatched episodes so far of is Go-onger due to the comedy.

for KR, I have rewatched episodes of Ryuki, 555, Blade, Kabuto, W, OOO, Gaim, Drive, Ex-Aid and Build...when i feel like it xD

I probably would have watched something from Boukenger or Kabuto the most apart from Power Rangers because I watch Boukenger Task 43 every Christmas as well!