No complaints really.
Amiga OS is classic, and is what it is. Is what I loved. Could have been developed further, but lost out to a sad fate. I know there is OS 4, but I've not played with it yet. No need to, all my classic stuff works great on my 80Mhz 060. So I guess there my only complaint is that it died and no new hardware or 68k development on the OS is going to happen.
MorphOS. I love it. No major complaints at all here.
AROS. With the right hardware, it's pretty cool considering it's free. I've a ton I could complain about it, but again, considering it's free and does what it can do as well as it does. I'm pretty impressed.
Looking forward to the Opus Magellan sources coming to fruitation on these OS's. Will be neat to see where it can carry things.