Next, 80, Nexus and the original '66 Ultraman are what got me into Ultraman, in that order. Though to be fair I was watching the original while I was watching the other stuff too. A couple episodes at a time.
And that CGI Trailer I found on Youtube that started the journey. I spent a day trying to find the movie that trailer went to (that doesn't exist),..but found Next instead and watched that. I liked it and that led to Crunchyroll and 80. Then I watched 80 and the original at about the same time. Then Nexus I thought was so good I pretty much binge watched it. Wasn't crazy about the final few episodes and the change in tone, but by then I was hooked on Ultraman. Then I watched the Zero Trilogy. Then just kept going.
Nexus, Mebius and Max really sucked me in though and I pretty much binge watched those 3 series.
I thought Ultraman was always popular I had no idea they'd had so much money troubles. I got the impression Kamen Rider and Ultraman were just huge and incredibly popular in Asia and everyone loved them. Which is why I was surprised that Ginga was so cheap.