Shrinkenger IS a a terrible show. It was one of my first Sentai Series and almost got me turn off from Sentai for good. Thank god, I watched Abaranger and Gekiranger and really got into SS.
Shinkenger doesn't make use of its theme even for 10%, its plot is okay at the best, it doesn't have any creativity whatsoever, except for that red ranger twist at the end, its villains are completely wasted, especially Judo, the only good actors are him and Takeru (girls' acting was literally unbearable for me. Romi Paku at her 3 seconds of being actually onscreen had more believable acting, than both of them in the entire season), team up with Go-Onger is one of the worst in the entire franchise with any Go-Onger barely in. And Hyper Go-On Red... No, please just no (team up with Goseiger on other hand is really good, but it's not exactly a plus for Shinkenger, but rather for Goseiger). Both movie and Returns are nothing, but a joke. Zords are awful. Upgrades are good, but other arsenal isn't. Shinkenger is trying to be one of 80s Sentai and fails miserably.
But to its credit, PR Samurai showed, that this is not the worst thing you can see. Actually it made Shinkenger pretty enjoyable in comparison.
Jetman is your typical Inoue show, but it had Gai and characters are different and not actually forgettable there, unlike most Sentai of that time blahblahblah etc. it's okay show for me. A fun ride for once, one can say.
IMO, better spend time on series like Liveman or any 90s Sentai. They won't disappoint.