I must confess, I've been very interested in this lens and anxious to read a review. Needless to say, I never expected it to even come close to the Canon 500 or 600 F4 IS's (of either the I or II generation), nor do I think did anyone else, even if the price came in at 2-3 times the now announced price. What I DID hope for though, is something that might at least match (or maybe even exceed) the resolving power of the 15 year old 100-400L and also provide a reliable auto-focus. Once the price was announced, that expectation was certainly made much more dubious, but I was still hoping they might pull it off, however unlikely that seemed. My two biggest fears would be that it would have lower IQ than the 100-400 IS and, even more so, that it would suffer from the perennial third-party lens sin of unreliable auto-focus. Much remains to be seen of course, as this is only the first review, but the troubling AF issues encountered by the reviewer certainly seem to indicate the AF may struggle and freeze, particularly at the long end. To me that is an even bigger deal breaker than IQ being less sharp than the 100-400L. Birds in general, and BIF in particular, don't give you many "second chances" to get the shot--AF just has to work. Lately Sigma, with its Sport and Art series of lenses are managing to change the expectations of users when it comes to both IQ and AF, and I was hoping that Tamron, with this lens might aspire to similar, lofty ambitions. Granted, this is only a first review and there hasn't been any side-by-side "apples to apples" comparison between it and a 100-400L, or 400 5.6L regarding IQ, and the AF issues might yet prove to be something wrong with this particular example, but the AF issues in particular are troubling, especially given the 5D III's stellar AF system. For those of us with cameras with lesser AF systems (even good ones like the 7D), it's bad news--if the lens can't focus well on a 5D III (or 1DX, 1D IV for that matter) then those of us with a 7D or 70D are going to have even greater issues--and then there's the AF systems on the Rebels!!!!!
Like everyone, I'll be interested to see Justin's review and even more interested to see Lens Rentals and Bryan's (The Digital Picture) reviews. However, it's starting to sound like this lens is aimed more at the level of the older Sigma and Tamron lenses, rather than the "affordable" L series or the Sigma Sport line. They may have "out bigma'd" the Bigma---but I was really hoping they'd set their sights higher.