Megaranger- His very first official work combined electronics to teenagers with an attitude plus a space base for these guys. So okay there were a few tributes like a slacker red ranger (Kenta), a collective black (Koichirou), a yellow ranger who is a photographer (Chisato but she's no rebel) and a pink airhead (Miu, the idea came from Carranger's Yoko) but the blue ranger Shun is so much well, a smarter male blue ranger (idea probably taken MMPR's Billy with an original twist). I could also say taht this was the show with the first silver ranger (Yusaku) which also managed to return a non-five piece combining robot as the primary robot. Overall, pretty much introducing the concept of blending the past and present IMO.
Gogo V- He succeeded in making a better sibling Sentai than Hirohisa Soda did. Okay Fiveman was a burnout, this one was blazing hot! He introduced the not yet repeated concept of family vs. family where both villains and heroes were a family. The Saima were the anti-thesis of the heroes as the heroes were a loving family, they weren't. So for a Fiveman upgrade, let's give him praise for this!
Gaoranger- This is where wild animals got fully utilized and the concept of multi-gattai was added. In here, his contributions would also involve changing main villains which all three were soon combined into the final villain Senki, a twist I think would be hard to replicate. Also, the series introduced the sixth ranger having a combining mecha, a concept reused in Boukenger.
Go-onger- This is considered his worst series but I say this series isn't trash either although Power Rangers RPM is better (for some). So he actually did combine Liveman's colors with the concept of Carranger's humor. The series contributed the idea of mecha that could go micro to macro size who can talk with their ranger owners (compared to just the bonding between man and dog type of mecha companionship), an environmentally focused Super Sentai and the first female extra member Miu (and she is also the first female silver ranger). This was the first Sentai that had a team of seven in the finale.
Any corrections? Feel free to comment and give sources!