I generally like the design of the Z better than that of its sucessors.
The soft-touch was great, aluminum is generally a bad idea when there are antennas nearby and it really destroys the look iam loving the Z for right now.
The plain black monolitic all-around, with the frame that is like pebble-blueish when looked at in the sunlight.
Just great imo.
For me the Z1/Z2 are a step back regarding the sleek elegant design that was inherent to the Z, except for a few changes.
The flap-less headphone jack is really the only thing that i really found to be annoying about the Z, and the 3200mah is also a great step forward.
Other than that there isnt really much beside hardware-specs that was improved in my opinion.
Still missing such a feature like IR, maybe with the Z3?
Display was always kinda okayish when looking straight at it, and due to the bad viewing angles i dont need any kind of "privacy-filter" foil or similiar :P
Things that should get improved is the Picture-Quality in dark conditions and in macro-mode i hate that blur-filter that seems to destroy any little detail i was used to see on a lot older devices.
There have been Sony-Ericcson's Cybershot phones that are now pretty much "historical" that took more natural or even in general better looking images.
Its also sad for me to know that my five year old phone takes better macro-shots
Anyways, we'll see.