I watched Power Rangers obsessively up until the end of the Lost Galaxy season. Most people I speak to on the subject point to Lost Galaxy as the tipping point of quality, being that it was the very first Power Ranger season to sever all ties with the original series. I remember liking it a lot, though, and upon retrospect, it still seems pretty intense. Lots of deaths in that season, a very prominent theme of passing the torch.
The MMPR video game is what really gets my nostalgia going, though.
Me and my siblings used to play the hell out of this one. For a game based on a children's show based on a Japanese sentai show, it's surprisingly good.