I've always liked NeXTSTEP's distinctive user interface. I wish we had a version that ran on modern hardware, similar to what https://github.com/trunkmaster/nextspace is trying to achieve.
Also, Steve Jobs in Exile, the most recent book about NeXT, is highly recommended.
Just get a modern Mac and remove half the RAM. That should get you the same experience. The visual design was first class, but I remember when I went from NeXTStep to NEWS to X11 and was very relieved to not have to have my mouse spin for minutes at a time.
To some extent everything was like that unless you had bleeding edge hardware. Running an up to date version of Windows was endlessly frustrating until the Core 2 Duo came along.
I have a toy recreating the visuals: https://github.com/mkmik/nextstop
(It's vobecoded in the original sense of the word)