The ranger games were fantastic just because they had so much... character. The teams were ridiculous. that made them memorable. The bad guys were interesting, the locales nice and varied. Seriously, one moment you''re in a volcano, the next you're underwater and then POOF desert. Then there was the load of interesting character designs.
Still the franchise has room for improvement. More varied permanent partners would be great, and they achieved that with Shadows. You wanna chill with a kricketot? Go for it. But then they took one step back and sacked you with fucking Pichu in the next game. Which couldn't even fight, it just used a fucking UKELELE.
The level design was also kind of annoying in that it was always the same. Find X mon to get past X obstacle.