I think the Amiga was way ahead of its time and inspired a fierce loyalty in its fans. Also, retrocomputing is a thing: working within the constraints of retro hardware has an artistic/hobbyist appeal of its own. This is what compelled me to buy a C64 again (actually a TheC64 retro clone with an ARM board inside. I've no patience for the actual difficulties of plugging ancient hardware into modern peripherals).

There's even an enthusiast's market for new games and software for retro computers. The target seems to be either people who remember them fondly from their youth, like me, or even people who were actually part of the scene back then! It's something like a club for old automobile collectors I guess.

As for uniqueness: everything about the Amiga was unique, especially when compared with PC and Macs (or the Apple II). The Amiga was built out of custom chipset purposefully designed for the vision its creators had; these were not off the shelf chips like with PCs.

For a pretty detailed history of the Amiga, complete with hope, betrayal and tragedy, I recommend you google the Ars Technica series titled "A History of the Amiga". It will provide a glimpse into what was so unique about the system.