I have been using OS X since it came out and have four Macs... three PowerPC and one Intel... and have never had to re-install the OS on any of them. In addition, I administer another 25 or so Macs (about half and half PPC or Intel) and have had to re-install only once on one of them... and the re-install took a little under 15 minutes. No applications had to be reinstalled and no data was lost. Applications, even on installation, are not permitted to modify system files. Essentially, I am saying that Mac's OS X doesn't get "buggered up."
Since a Mac can also run 100% of all Windows software either AS a Windows computer under Boot Camp, or in virtualization under Parallels or Fusion, it can certainly do everything a Windows machine can do. However, most Mac users find they will use the Windows side less and less as they find that the Mac solution is generally better and easier to use than the Windows solution.
Games run best under Boot Camp... Virtualization has about a 5-8% speed hit because it is running under/with OS X. Keep in mind that games that require the cutting edge graphics cards may not be as snappy on a Mac as they would be on a Games optimized Windows PC because the graphics cards a Mac are not really intended for high speed graphic games.
For the everyday user, the Mac can do everything they need... surfing the net safely (as of today, seven years after the introduction of OS X Server and six years after the introduction of OS X for the desktop, there are still ZERO virus, Spyware, and Adware in the wild for OS X!), safely open any email, download anything from safe sites without fear, and even run your computer without AV or anti-spyware. No software can be installed on your Mac without your permission including spyware or viruses. There is no Registry to get corrupted. Unlike on Windows, defragging is done in the background automatically and transparently with no user interaction... as are almost all other housekeeping chores. Microsoft Office for Mac is reportedly better than the Windows version... but Apple's own iWork suite is far cheaper and unless you are a power Word user, Pages will suit most people. Apple's Keynote beats MS Powerpoint hands down.
Security wise, at worst, any invading malware, if there were any, would only toast your user files and never touch the system files or any other user's files. The core of Apple's Mac OS X is an industrial strength FreeBSD UNIX which has been tested and fixed over almost 40 years of development in the open source community.
As Texas Booster said, the Mac is not intended for the do-it-yourselfer who loves to build his own computers or who wants to upgrade continually. However, Macs have a far longer than PC life expectancy. Macs that rolled off the assembly line 9 years ago using the old OS are still providing service today running OS X. Six your old machines can run the latest version of OSX... OS X.4.10... with no problem. Upgrades to OS X consistently result in faster application execution on the same hardware... sometimes remarkably faster execution on the order of 15-20% faster... where Windows upgrades most often result in slower execution of applications.
The final thing is that Mac users actually enjoy using their computers... they don't have to fight the computer to get work done. They don't have to wait for startup (when I do restart my Macbook Pro, it is ready for me to work in under 18 seconds... but most of the time it's just asleep and is ready in under 2 seconds...), they are not experiencing slow downs due to the overhead of the anti-ware downloading and scanning all the time... and they never experience the Windows rot that slows down a Windows machine over time. The Macs just work.
I keep about 60 PCs running for various folks, most of them older citizens who email and surf. I will assure you that most of them would be better served with a Mac. It might even be cheaper for me since I seldom charge them for the time I spend keeping their systems running.
I have helped friends reinstall OS X at least three times. I have reloaded Winders ???? times.
If you find a modern iMac, it should meet your needs. If you really want a cutting edge video card then get a Mac that allows replacement of the card.
In most cases the most recent Macs will be fine.
I've a G4 Ibook...that I purchased second hand. It was a leased machine.
It works fine...but I wasn't given the password..( The seller didn't know it..) to operate many of the laptop functions.
I've called Apple about it...but they act like they really could careless about my problem. Or they say send it in...but we might have to change the HD, or the OS for $600 or so. That's crazy....
There has to be a way to change a person's password....if they've forgotten it. Doesn't there?