2. ability to run virtual Linux servers are bare metal speeds (and their applications).

3. simple and easy container management of 1. and 2. with imgadm and vmadm.

4. OpenZFS - easy capacity growth, checksummed data, silent data corruption detection and self healing.

5. lightning fast, faster than GNU/Linux performance on the same hardware.

6. same application portfolio as GNU/Linux (14,000 applications available with a simple pkgin command invocation).

7. ability to create virtual routers and switches out of thin air with dladm, join and partition physical links in terms of percentages, simplifying network topology in virtualized environments.

8. OS paranoid about protecting and self-healing itself and the data it hosts.

9. ability to pick between KVM (slower) or bhyve for paravirtualization of non-Linux OS's like Microsoft Windows, OpenBSD, FreeBSD et cetera (although this process is poorly documented).

10. NFS V3, V4, fiberchannel and iSCSI which work correctly.

There is one major downside (I don't consider it as such, but I know others do): one must pick the hardware compatible with SmartOS from the Joyent's hardware compatibility list, not the other way around: https://eng.joyent.com/manufacturing/bom.html.

But when it does fire up over the network and once one groks it, holy shit, it's like being taken into the future with a time machine.