In my opinion the runner-up in terms of visuals is actually 10.4 Tiger, though — the dark grays ubiquitous throughout 10.5 and 10.6 have always felt kinda dingy and depressing in a similar manner to the dark gray Windows 95/98 (which, as an aside, is why I find the Windows 2000 variant of that look preferable, with its base gray being lighter and more cheery). That said I miss the 2D grid that 10.5 and 10.6 used for virtual desktops even today… the simplified 1D linear virtual desktops that’ve been in place since 10.7 feels needlessly watered down.
Funny enough that version of OS X can also run what to this day I’ve found to be the best implementation of a Quake terminal anywhere, in the form of the haxie Visor/TotalTerminal which added this functionality to the Apple terminal. The way it handled window focus and everything was so smooth and better than iTerm’s as well as any of the Linux dropdown terminals I’ve used.
On the note of Linux, I wish that there were Linux DEs that went the extra mile to produce a true OS X 10.4-10.9 analogue, but no such thing exists. The closest is elementary/Pantheon which is stylistically in the same ballpark but shares too much of its design roots with GNOME’s oversimplified iPadOS-like design. Everything else in the Linux world is Windows-type desktops or minimal WMs, both with flat UI themes.