The 200 f2 is my bucket-list lens purchase, my if-not-now, when? splurge, and after using it for two months, I am greatly impressed with its performance.
I considered getting a used 200 f1.8 for around $4000, but decided that having IS, a Canon warranty, repairs by Canon if needed, and a newer, lighter design were worth the extra $2000 in the long run.
In shooting dance and theatre productions in highly variable, often dim lighting, I have found the sharpness and IQ of the 200 to be significantly better than that of my trusty 70-200 f2.8 zoom, to a degree I would not have thought possible.
The IS works amazingly well, and enabled me to get presentable shots of the chorus in a recent musical who were positioned on the stairs to the stage, illuminated only by a bit of random light spilling their way.
One small gripe: Canon could safely assume that any shooters buying their 200mm to 800mm primes is using Arca Swiss-style plates (RRS, Kirk, Wimberley, etc.). Why not build a double dovetail into the lens foot to eliminate the need to buy plates or replace the entire foot?
That said, I love shooting with this lens, and am looking forward to the upcoming volleyball and basketball seasons even more than usual.