Well,
For me it was the cheese wedge design, and cream colour casing. Most PC are silver and grey nowadays.
It still rocks with its ease of use, and that Amiga OS takes a couple of second to boot up, rather than an is eternity.
The feeling that you could access directories and files easily with no 'hidden' programmes running in the background. The archticture and design is fine and effiecient, and multitasking is great on the Amiga.
It's way more fun to use, and i hope Amiga will get made again, once the technology becomes innovative and chip/processor manufactures work on design, architcture rather than speed, dual core, quad core etc..! Simplicity and style is key :-)