The OS is different, but I'd say it's hugely similar to the Amiga in some ways, particularly the support for a good graphical and excellent command line interface.
Finder is the Mac's achilles heel: it sucks. Badly.
Once you get used to the rest of it, it's wonderful but Finder is awful.
Other than that, I think it's a wonderful OS and the better support for full screen apps is a damn fine thing.