First the good:
Since purchase, I have had no problems with the lens whatsoever. It appears to be sturdier than most lenses on the consumer market, and that is a big bonus for nature photographers!
The F4 might be a bit slow for people shooting in low light, but for outdoor work, this lens shines every time. Colors are lovely, DOF is magnificent....your subject literally "jumps" out of the photo!
Now the bad:
The lens hood is butt-ugly. It looks like an afterthought (or worse, an after-MARKET item) that Canon put no imagination or time into designing. If you are going to make a white lens, and mark it "L" series, make the lens hood look nice....this looks like someone put a Ford Pinto hood on the front of a Corvette!
Finally, if you spend $500 or more on a lens, Canon should realy have sprung for the tripod mount. C'mon Canon, it's a piece of heavy plastic with a metal ring inside...THROW IT IN! Why should I pay another $150 just to secure my lens on a tripod. How cheap.