[Fish Sandwich]

There are so many good starting points I don't think you can go wrong, but my particular suggestion is that, if you're curious about the history and lore of Ultraman, Mebius is both a wonderful show in its own right and a great crash course on the Showa era Ultramen while still remaining accessible to new viewers.

To put it simply, it was Gokaiger before Gokaiger, but Mebius makes the guest appearances by past actors a bit more of an occasion, with the early stretch especially focused mostly on Mebius himself, which, again, keeps things accessible. Even more than the guest appearances, I think the show represents Ultraman on a thematic level perfectly. If I had to pick one show in response to being asked "What is Ultraman?", Mebius would be it without a doubt, and as a big anniversary celebration, that's how I know they did their job right.

Still though, don't feel too obligated to pick it if something else seems more interesting to you.