:|
As DCAmiga is saying, you don't need an operating system at all to run games on your Amiga 500. You just need to find someone who has some games (and a copy of workbench 1.x or 2.x) for you to try out. Many people throw away their old disks nowadays because they have hard drives installed with something called WHDLoad that runs games as 'virtual devices'.
If you like what you see, and/or want to dive deeper, dont mind fiddling around with hard drives, file systems, and the Amiga operating system, I think you should forget about your amiga 500 and go with either a a1200 + hd + 030 accelerator, or a4000 + hd.
Please dont take that the wrong way. Expanding your A500 into a usable machine (I mean something that does more than play some old games) is expensive and bound to frustrate you.