This lens would be an excellent value, except that I can't seem to get my hands on a reliable one. After all the different times I've purchased this lens, and all the times it must be sent to Canon (at half the price of the lens each trip) to fix the sticky focusing mechanism that will lock up at the most inopportune times, I could have just bought the 1.2L!
I think it may have been a bad omen when the very first time I bought this lens new from KEH, the autofocus was Dead On Arrival and had to be returned.
Even with the autofocus reliability issues, some of my best photos were taken with this lens. I won't dump another dime into trying to get them working correctly though. They will just continue to malfunction 2 months after the 6-month repair warranty has passed.
I would only recommend this lens if you like taking a gamble. If/when it works, it definitely shines! I would definitely have a plan B if the photo matters though.