Gekiranger is considered by many to overall be one of the better modern sentai series, though it is all a matter of opinion. I can honestly say when I first saw the Geki costumes I thought "WTF is this", but the series I think is quite good if you go into it open minded. In my opinion Retsu, Ran and Ken are bleh as characters. Gou I only liked because I thought he was cool (but the character overall isn't great either).
The characters in Geki I really like however are Jan, Rio, Mele and Long. If you're at Lesson 31 and still don't like it then you should probably move on.