@STUser
OS4 will run most software that runs on modern classic Amigas. A basic A1200 is not a modern classic Amiga, but an A1200 with a fast accelerator and a graphics card is reasonably modern and most software, including games, that works on one of those will also work on OS4.
As long as your system isn't already badly outdated, the transition will be fairly smooth. The OS itself has all that OS3.9 does, with a lot of improvements.
There is UAE of course for old games and stuff, but it will need an update.
