If I had to give up all but one of my UAD plug-ins... well, first, I'd refuse, but we're just being hypothetical here, so what the heck!
Ocean Way Studios makes changes to tracks that no other plugin I've heard can do. It is not always the right change, you can make sonic magic, or sonic garbage. When it works it is almost magic.
I never worked in the Ocean Ways studios, so I do not know what they sound like. Thus I can not say that the plug-in is accurate. What I can say is that selecting different microphones, and moving them around creates an aural image that is very pleasing. I'd say it sounds natural, in that sense that it sounds like the track was recorded in a nice room.
A couple of caveats...
First, as brilliant as re-mic mode is (and that's what I was describing above), the reverb mode is much more limited. Possibly I just haven't figured it out, but whatever the case, I use re-mic mode unless I'm just dinking around. I do seem to be somewhat alone in this opinion.
Second, and others have commented on this as well, re-mic mode works a lot better (or is easier to use?) with tracks you've recorded yourself. It takes quite a bit of patience to get it to sound good on sampled instruments. Which makes no sense, and yet there it is.
Now recently I picked up Cinematic Strings 2 (and really wish I'd bought it a year ago!) and for some reason I found it much easier to place those strings in OWS. I started with their Room A Strings preset and didn't do a lot of tweaking after that.
Chris Hein Horns Pro Compact (that's a mouthful!) took me forever to match to OWS. It was worth the effort, but I do wish it had been easier (of course the biggest difference - ignoring that it is brass & winds vs strings, and two different developers - is that I had a deadline when I was working with CHH<G>).
Anyway - OWS is a brilliant plug-in that can do a wonderful job of placing a track, and even a sample library track, in a very nice sounding space. It will not replace a reverb, but it adds some ambiance that is aurally pleasing.
You will almost certainly still want to add reverb - I've found that OWS should proceed any reverb, and that algo or convo doesn't seem to matter, and that plates and chambers seem to compliment OWS nicely. Although if you are going for EFFECT you can use almost anything<G>!
Have fun!