The comparison may be a little anachronistic but... well, in order to understand why OpenVMS made such a dent on computer history, you have to put it in context first.
OpenVMS's days of glory more or less coincided with the Unix wars. Unix was brilliantly hacker-friendly, but a lot of basic things that we now take for granted in Linux -- virtual memory, high-speed I/O and networking -- were clunky and unstandardized. Others (like Files-11, VMS's excellent filesystem) were pretty much nowhere to be found on Unices (or, if they were, they were proprietary and very, very expensive). An Unix system included bits and pieces hacked together by people from vastly different institutions (often universities) and a lot of the design of the upper layers was pretty much ad-hoc.
OpenVMS had been a commercial project from the very beginning. It had a very well documented design and very sound engineering principles behind it. I think my favourite feature is (well, technically, I guess, was) the DLM (Distributed Lock Manager), which was basically a distributed concurrent access system with which you could do concurrent access to resources (such as, but not only, files) in a clustered system. I.e. you could acquire locks to remote resources -- this was pretty mind-blowing at the time. You can see how it was used here: e.g. http://www3.sympatico.ca/n.rieck/docs/openvms_notes_DLM.html .
Also, the VAX hardware it ran on rocked. The whole thing was as stable and sturdy as we used to boast about Linux in comparison to Windows 98, except at a time when many Unices crashed if you did the wrong thing over NFS.