If you really want the look and feel of the classic Amiga try Amiga OS's 1.x through 3.x. You can try them out in WinUAE. (You can legally get the ROMs from Amiga Forever
http://www.amigaforever.com/ ).
Classic hardware (Amiga 500, 2000, 1200, etc..) systems are rare but cheaper then buying a new Amiga OS 4.1 system. Once you have a classic system the options to expand and enhance them is plentiful. Personally, the only way to get that retro nostalgic feel is on the classic systems.
