This is really a 5-star app for physicians with a Mac. I've been using it since the 2.x days, on OS 9, and love its power and elegance. For the past 5 years or so, I've also paid for the "64-bit" extension to support the developers, even though I have no use for the extended memory management (I only view angiograms, which are not resource-intensive).
My major gripe is that its free version stamps all images with a "Not for medical use" watermark, which is truly annoying.
This, in effect, forces even light users like myself to upgrade every year to the tune of $150-250.
Now that my license has expired, I decided not to renew it for this reason. I believe it's ill-conceived; hence the 4 star rating.
Hope Antoine reconsiders this watermark thing.