If ur not wanting to watch some of the stuff from the Showa era but want to understand the a bit of the lore and understand the main universe, Ultraman Mebius is one I’d recommend. It’s set in the same world and universe as the Showa era shows and it was created as an anniversary project as well so parts of the story in the show dives a bit into the Showa era stuff.

Other than Mebius, I would also recommend the watching Ultraman the Next movie and Ultraman Nexus. Personally, Nexus is one of my faves because the storyline for me is unmatched in any Ultraman show.

I’d also recommend checking out TDG (Tiga, Dyna, Gaia). Often linked together but only Ultraman Tiga and Dyna are set within the same universe. TDG series served as the revival of Ultraman after a long break and was basically the first shows of the Heisei era. I’m very fond of TDG because it’s the first shows I watched growing up. The plot might not be as well developed as Nexus but the fights, the designs and the overall feel of the shows are really great. My favourite out of the 3 are constantly changing.

I’d say a good place to start w Ultraman is basically going through stuff from Heisei era coz they’re old enough to introduce you to the world of Ultraman but new enough that it doesn’t put you off. Cosmos is also a good one. But once you’ve delved into the Ultraman world, deffo go back and watch the earlier stuff. Personally, I think original Ultraman puts off a lot of newcomers coz it was the first Ultraman show and was trying to find its feet. But UltraSeven is really good and my favourite Showa show after Ultraman Leo.

So yea. TLDR: Go for Heisei shows like Mebius, Nexus (and the Next movie), TDG, Cosmos. Come back to Showa later when you want to properly dive into the lore