They are lighthearted, but that's not necessarily a bad thing -- it depends on how it's done. But I think sentai's stuck with the lighthearted type too long -- it needs shaken up (and Boukenger certainly wasn't the answer when it wasn't too terribly different from the other recent shows). Den-O's lighthearted, but Rider really needed a lighthearted entry, IMO.
Ok, what about Hurricanger? Since Goujira showed up, it became a little bit darker or what? What about... Yousuke's nearly death, trying to save Ikkou from Mahaburara's (sp?) poisonious scorpion? Some episodes were the best ever.
Ok, I admitted that Hurricanger had some light-heart because of Shurikenger, Oboro, Wendinu and Furabijou. I loved them all.
Hurricanger is one of my favourite Sentai series, next to Dekaranger. Unlikely Ninja Storm's stupidity bullshit.
How about Abaranger? Since AbareKiller first showed up, it became DARKER and intense violence. I loved the story between Ryouga and Mikoto. The battle between AbaRed and AbareKiller were awesome. Abaranger is an awesome Sentai series, effin' better Dino Thunder and that's for sure.
Dekaranger? I loved Dekaranger and I admit that Ban and Umeko are both silly but they are both my favourite Rangers. Umeko is more than Ban for me, IMO. She's hot. Anyway... what about Jasmine's past, the one who told a story about when she was a kid? That was dramatic and dark. I can't remember others. Personally, I prefer Dekaranger better than S.P.D.
Magiranger. Yeah, Magiranger isn't the best sentai series ever, but it was good. I liked the story about 5 siblings and their parents. Wolzard's past and everything. The talkin' plant annoyed me a lot. I understand that Magiranger had too many silly.