I started actually watching Sentai from Gokairanger and watched it start to finish.
I also watched Go-Buster start to finish, fascinated by Enter and the whole sci-fi vibe.
I stopped watching Kyoryuger after the gold ranger arrives. His henshin scene just looks ridiculous and there is no characters that just clicked with me. The villains are simply to far away from the whole Dinosaurs theme.
I never watched ToqGer. Their designs are too stupid. The mechas are not interesting.
Ninninger, on the other hand. makes me watch it week after week. Why? Probably due to Kyuuemon, Kasumi, Nagi, and Tsumuji. Kyuuemon truly exhibits the trait that Enter had: calculating, scheming, trying. Kasumi feels like a truly smart character, except when the writers make her generic due to need to promote Takaharu (blegh). Nagi simply feels like the heart of the group and stay true to that role awesomely. Tsumuji feels like the innocence that ground the series. Hopefully Zyuohger can at least give us a new Enter or Kyuuemon so I can watch the character develops and watch the sentai start to finish. Ghost simply doesn't attract me anymore due to lack of interesting characters. Drive has the quirky captain, Mr.Belt, and Chase.