@macto
Compared to Win95/NT4.0, ~1995 era OS/2 Warp’s GUI is ugly in my POV(one of many issues***). I didn’t like BeOS due to the initial lack of software, legacy support and GUI issues i.e. BeOS didn't impress me at all.
MacOS X has most of the Win32 critical applications and games for a real alternative OS. The barrier to MacOS X is likely be to hardware issues i.e. lack of secondary HW sources("out of the box"*) and uncompetitive mainstream** HW prices (not factoring X86 premium product lines).
*MOL on PPC clone issue is unacceptable in mainstream.
**Price points (to illustrate an example), 2 Ghz AMD CPU or Intel PIV 2.8/3.0Ghz and motherboards i.e. cheap/barebone VIA, NVIDIA and SIS based.
***Early issues with Win16.