I've had my 21.5" mac for about six years and had been contemplating an upgrade for about three.I sure am glad that I did!This 27" is a world of difference from the 21.5" version, and with the extra 16Gb of memory, it is Lightning fast, smooth, and renders nothing less than STUNNING 5K video on its large screen.Everything is so much faster, crispier, and efficient, and apps and programs run remarkably smooth.The migration process was painless, and AppleCare was right there along every step of the way, providing much needed guidance and instruction to ensure a smooth transition.If you are thinking about upgrading from a smaller screen(21.5") or from the horrors of the Windows platform-DO IT! you can't go wrong with this computer.I would recommend a minimum of 32Gb of memory to even get you started with this machine, but the value and advantages of doing so greatly outweigh the relatively minor cost of the memory modules.Hope this helps you with making probably one of the best personal computer-based decisions you could make in these times of rapid technological changes and the worry of CONSTANT expenses for simple additions on OTHER platforms.