Another fun thing about the Showa Gamera Series is, if you get right down to it, I always thought that the first three Gamera films at least were pretty vengeful, dark and brooding, especially for kids' films (yep, before Gamera officially became a hero, the kid characters were pretty angsty, which I totally identified with)! Gamera Vs. Viras (one of my top-favorite Gamera films) set the pace for the more happy & cheerful entries that I'm sure everyone is more familiar with!
But other than that, I agree! The old Gamera movies are still pretty fun!