My own thought:- Well first off the spell checker is limited as it uses US English, so for those of us using International English, words like colour, tyre, jewellery, centre etc are always going to come up as mis-spelled words. I would rather have seen buttons to align text left, right or centre instead. A lot more useful tool.
Although there are now extra fields for options, the ability for putting cost variants on options limits this facility. Although this will be incorporated in the pro version, this is something that should really be in the basic version, as even free carts out there offer this functionality.
Themes, I would have like to have seen all the previous themes retained and the new themes added as an extra. Seem to have less themes available now which isn't good news for the folks that don't want to invest in the imminent release of the new themes designer.
So what are your thoughts? What do you like and what don't you like in 3.6?
