Big improvement in IQ between version 1 and version 2 IMHO.

I think Version 2 has a closer minimum focus which makes it useable for "macro" work although its not a true macro lens.

Version 2 will accept the 1.4 TC which takes you out to 560mm focal length....the AF and IQ hold up very well using the teleconverter.

Version 2 zooms with a rotating ring vs push-pull for version 1 .... I think this is easier and more intuitive to use and it has been reported to reduce internal dust compared to version 1.