This release has been long in the making, as rumours, hints, and then definitive confirmation of a MorphOS port to the PowerPC Mac Mini started appearing a long time ago. This port works on all variants of the PowerPC G4 Mac Mini (so not on the Intel Mac Mini, obviously). Installing MorphOS on the Mac Mini is pretty much the same as any other operating system: hold down the 'c' while the MorphOS disk is in the drive, and go from there. This guide will help in setting up a dual boot environment with Mac OS X.
This release also includes a lot of bugfixes, but as a relatively inexperienced Amiga/MorphOS user, nothing really stands out to me. It's a long list in any case, so that's a good sign.
The upgrade is free for existing MorphOS 2.x users, and there's a demo version available so you can try it out, but without the keyfile it will slow down after (I believe) 30 minutes of use. This is a good way to find out if MorphOS is worth your money. Speaking of money - MorphOS costs 150 EUR, which includes VAT.