I owned the first version of this lens for ten years or so and was always impressed with the results.
I sold that lens on the weekend for $1200 Canadian (ouch), and picked up a used version II today. It looks brand new. The only missing from the sale was the box.
But when I put the lens on my cameras, I noticed that the Image Stabilization is noticeably better than the V1 of the lens. But moreover, this lens is INCREDIBLY sharper. Maybe my V1 lens was a dog, I don't know. This one blows my old one out of the water, though in reality it's just a small improvement - but improved enough I can see the difference on the camera LCD.
I put a Canon 1.4X II TC on the lens, and the AF seemed just as fast. Not so with my older V1 lens.
I'm very impressed. Now I have a 100-400L IS to upgrade (ouch).
I think it was worth the difference of $800 Canadian that I paid to upgrade, but maybe I'm just crazy.
I don't think you can go wrong with this lens, particularly if you like making portrait shots, and especially for indoor sports like ice hockey.