Great series. 2007 was the year I officially considered myself a Toku fan, and like Den-O is my favorite Rider series, Geki is my favorite Sentai. I honestly liked Jan the jungle boy from day one, and actually enjoyed his "Jan-glish", his fiery spirit, and his determination when the chips were down. The show was really good in how much of it focused on the training and development of the Geki Jyuken team, and the way they earned their new powers and abilities.
The drama and tension the series had was top-notch, and the show was very good at portraying the family ties throughout the series. However, it was also able to balance out the light-hearted and dark parts quite well.
Of course, being a martial arts sentai, the fights were excellently choreographed, and the mecha battles were quite enoyable in the way they were like giant martial arts matches, as well as the G Gundam-esque way of controlling the robos.
Gekiranger is a series I'd reccommend to any sentai fan, and definitely one of the best