Madoka was pretty light hearted and even ended on that note.
The issue with the whole reputation thing is that fans will know the reputation, but the average person won't when they're buying. Plus if they do research where are they going to go? There aren't English speaking places on the internet outside of /m/ and a few forums like here that have seen Super Sentai (or toku in general), let alone have detailed reviews that indicate "hmm this series is bad!". In addition very few fans have seen pre-Jetman sentai outside of Sun Vulcan, Maskman, and/or Liveman be it nobody subbed them or subs stop during progress (still waiting on those LITERALLY TWO EPISODES of Changeman that nobody is touching to make it complete). Let's not forget that Zeo holds a lot of nostalgia for people that grew up with MMPR (me included), they're going to be interested in what Oh was like not unlike those interested in Zyu/Dai/Kaku forming the original series. We shouldn't just go with a mentality like "I don't like Ohranger, therefore it must be skipped!"
As for pre-Zyu series to go with? Shout could go for Battle Fever J, Denziman, and Sun Vulcan. Why? Those three have the Marvel label on them. Release them as a Marvel Sentai trilogy or something. That way you can aim for comicbook fans too.