Grom is an chain in Italy, but even though they probably have dozens of stores there and various other parts of the world, they pride themselves on the philosophy of using artisanal methods and only the finest ingredients. I had a pure dark chocolate and a straciatella (like chocolate chip) when I went to the shop in Florence a year and a half ago, and though I remember being happy with it, it doesn't stand out in my mind the way the Vestri or the Vivoli gelato does (I was on a mission to eat as much gelato as possible when I went to Florence, and I didn't do too badly). However, as it was the first gelato I ever tried in Italy, my memory may be distorted by the many, many cups of gelato I've had since. In Florence, the lines were just as long as they were in Tokyo, even though the shop is hidden away on a side street near the Duomo. The Tokyo Shinjuku shop is much more glamorous, being on the street level of a department store (not relegated to the basement or top floor the way restaurants usually are), with trees all around and crystals dangling from the ceiling. It's definitely a good place to see and be seen while waiting in line, the trendy way to beat the summer heat.
Shops in Malibu, New York, Paris, and Tokyo
and across Italy
Shinjuku Marui Honkan Bldg., 1st floor