Well, basically for two reasons:
1) This Cover:
I lo-o-o-o-o-ove this one. I love this issue, featuring for the first time ULTRAMAN and the Crime Syndicate. And I love the sweet worried Black Canary of the cover.
2) Because Grant Morrison used ULTRAMAN in his JLA: EARTH 2 to reaffirm the superiority of Silver Age mythos over the boring, dull, "realism" of post-Crisis DC.
Long live ULTRAMAN!