(picture from Engadget)
One glaring con for me is the lack of a microSD card slot. I still don't understand why they do that (as with Google's Nexus series). The explanations for controlled environment etc just don't counter the convenience of expandable and switchable storage. I think it's one of the reasons why Samsung's Galaxy series does so well because they still have microSD expansion.
HTC says availability is mid March... but since that coincides with Sammy's rumored announcement... I don't see people rushing to get a One when they can get the IV.