Everyone is talking about how great the GS/OS is for the Apple
IIGS. Sure, it looks good, and it's rock solid,
but I think I'm going to stick with ProDOS for a few reasons.
Sure, It Looks Good...
The GS/OS has a GUI much like that newfangled computer called
the Mac Plus, but it's
better. Not only does it have beautiful colors, but it supports all
kinds of new innovations, including AppleTalk, 3.5" disks, and huge
hard drives. These new innovations require hefty system hardware, so
users of Apple ][, ][+, //e, //c, and other non-GS Apple IIs can't run
it. Even users with GSes can't run it if they don't have a lot
of memory.
Files Everywhere
The GS/OS scatters files all around your disk, mostly in this folder
called 'System.' Within it, there are folders called 'FSTs', 'CDEVs',
'Drivers', 'Fonts', 'System.Setup', and 'Tools'. Within these folders
are tons of indistinguishable files. Really, you don't want to mess
with this folder at all, otherwise, you could mess up your
IIGS.
Installation
The GS/OS comes with an installer that is also used to update your
computer, as well as install some third-party programs. This makes
installing/updating/removing things very intuitive.
Older Apps Still Run - Sorta
Your older Apple II programs run in an environment that actually
starts up the old ProDOS familiar to most Apple II users. However, some
programs do not like running in this environment and crash.
Old Formats Gone
The older DOS 3.3 format is now unsupported by GS/OS, so any
older disks you have can't be used. This makes for many
inconveniences.
Conclusion
Apps written to run natively in the GS/OS will be impressive,
offering color graphics at high resolutions, sound, and more. However
with older app support being spotty, and GS/OS requiring a whopping
1 MB of RAM and at least 600K disk space, it's not for
everyone.
New technologies are sure to leave people behind, but this means
that most will have to buy a new computer. 
