To be fair, Nexenta is probably the best solution right now for storage if you want something that's really third party. But...
1) It's fibre channel support is horrible
2) It's FCoE support is utterly awful
3) It has great NFS support, but it's SMB support is kinda half assed
4) It's user interface is archaic and barely usable.
5) It's options for backup and management just isn't very good
6) It's support for things like VAAI NFS is present... kinda sorta.. it's just not there
7) Support for OpenStack storage is ok, but it simply doesn't offer anything you can't just get with Ubuntu or RedHat running swift and cinder.
8) It's iSCSI target isn't great. It's better than Microsoft's but that's not saying much.
9) It's yet another system to manage and just doesn't have the integration that modern data centers should expect
10) It doesn't have PowerShell or PowerCLI support. It doesn't have full vCloud Orchestrator, System Center or UCS director automation support.
11) It's REST API looks like it's documented with a 4 year old with chocolate all over his fingers.
12) Calling or mailing support at Nexenta is a gamble. You might as well google the Oracle docs for Solaris since Nexenta is simply not likely to respond with anything more than an offer to sell you something.
13) At some point, Oracle will probably sue the hell out of Nexenta for license violation and it won't matter if Nexenta is in the right or not. They'll be lucky to keep their heads above water throughout the lawsuit.
Don't get me wrong, I LOVE ZFS and use it in my production environment since it's by far the most incredible solution out there, but I just don't see what NexentaStor has to offer other than a REALLY expensive storage stack with tons of half implemented features.
If you actually think you need NexentaStor, you haven't done your research... while I think they'd make a good $99 storage system, I couldn't imagine paying more than that.
Sadly, while there are hundreds of cheap and crappy Linux, BSD and Solaris storage solutions out there right now, Nexenta might be the best of the cheap and crappy. But for OpenStack, the stock SWIFT and Cinder solution is best. For Windows, Storage Spaces is truly the best thing ever made. For VMware ... there is no good storage solution for VMware at the moment. For some reason, VMware decided that they would focus on another generation or two of legacy crap packaged as a $2500 per CPU add-on. You almost have to use a SAN appliance from EMC, NetApp or Hitachi to even keep your head above water there. Nexenta could fit that hole, but unless you want to use some fairly odd SuperMicro twin servers for running Nexenta, there isn't many good hardware solutions for hosting it out there.