With the release of Synapse's OB-Xa clone today, I figured it wouldn't be long until the topic came up here, and comparisons to hardware synths drawn. Arturia's recent offering (OB-Xa V) has gotten tepid reviews which pretty much reflect my thoughts on it.
I figured the best way to assess it was to compare it side-by-side with my OB-6. Overall for $100 I'd say it's well worth it, and almost surely the best vintage poly plug-in I have in my collection. I will say that in order for it to truly be in the same ball-park with the OB-6 side-by-side sonically, I have to put Kazrog True Iron (transformer saturation plugin) on it to add the warm and fullness, but when I do the sound is surprisingly competitive with hardware.
That said, not only will I be keeping my OB-6 keyboard, but may add a second desktop at some point (if I can ever decide between a second OB-6 and a Prophet 6 that is).
But yeah, for $100 plus a little external warmth added? Definitely recommended, and a great supplement to any Sequential DSI synths you may already own. Plus, it could be considered sort of a simulation of what it would be like if I could click a button to toggle between 8 and 16 voices on my OB-6

One nice thing is that they didn't go nuts with features and add a bunch of things that you'd never find on a vintage Oberheim that dramatically diminish the character of the instrument. Interface is spartan, and much more tweakable IMO than OPX-II (which I also regard highly).