As always anything Amiga-related brings out the preachers saying what others should or should not do - particularly whether things should be allowed to live or not. As most Amiga history is, the story of MorphOS is convoluted. But let's instead look at what it does and what it can offer to those interested.
First of all it's Amiga-compatible. Out of the currently available "next-gen" AmigaOSes, it's probably the most backwards compatible. Now this obviously only matters if you already own Amiga software or like what's on Aminet - which means you're likely an Amiga user already and get what it's all about anyway.
Everyone else might find it interesting because it's lightning fast even on these older machines. I am actually typing this from a 1.25 GHz G4 Mac Mini with 512MB of RAM, and it's every bit as responsive as my i7 Mac Mini server with 16 GB of RAM. In fact it boots and launches the apps I need much faster (if both are turned off - the server usually isn't).
Why you might like it:
What it is great for is general surfing, mail, light productivity and such. To an extent a lot of the same stuff your typical Linux distro is good at. Except faster - even faster than something like Puppy Linux or DSL. It is quite easy to learn your way around like the other Amiga-based systems - far easier than the mainstream operating systems IMHO.
It has a lot of nice apps built-in like CD/DVD authoring, text editor with syntax highlighting, basic music player, picture gallery software, CD-ripping software,FTP/SFTP client, PDF viewer and a Webkit-based browser. It also has some a very lovely SSH client, some very good IRC clients, some nice VNC and RDP clients, lots of emulators, a lot of games and game ports, graphics software like Blender and much more. A lot of the same goes for other Amiga-like flavours and both MorphOS and AmigaOS 4 can run a lot of older Amiga apps out of the box as well. There is also software actively developed by third parties like Hollywood from Airsoft Softwair which I cannot say enough nice things about. Publishing software like Pagestream is also still maintained.
In other words you have a functional and fast computer out of the box and you can explore a lot of software afterwards. OS geeks should have as much fun with this as with Haiku, various BSD and *nix flavours and so on.
Why you might not like it:
Your kids want the latest and greatest Flash games. You want to watch 1080p video (not really an OS limitation but rather hardware). You want to run a server or have a multiuser environment. You absolutely cannot tolerate a crash (while I have yet to see a system crash, there is no memory protection. It IS very stable, though). You're just not curious about other operating systems and like what you have.
It should also be noted that WiFi support is on the way, and like previous updates it's likely to be free. Yes, the entry price is somewhat steep, but historically a one-time purchase (license is tied to the machine) gets you all subsequent updates for free. I bought it at 2.5 if I remember correctly and have not paid anything since. That's pretty decent value to me.