Having pretty much not played Tropico since the very first entry (bought the 4th when it was on error-sale for 99% off, but bounced off the UI), I tried the free beta weekend of Tropico 6 earlier this month and was rather impressed. Managed to screw up my first beta game by overspending on military in the cold war era to keep the generals happy, which seems a fitting way to lose.
The UI is loads better than 1 and 4, being much more intuitive and easier to navigate. After playing the free beta I gave 4 another shot, only to be convinced it was worth getting 6. Relatedly, from what I've read they've made some good changes/refinements both to the UI and other features in response to the beta feedback, which is always nice for a developer to do.
In terms of the touted new features, I agree with Rock Paper Shotgun on the islands -- it doesn't seem significant at first, but over the course of a game it does help break up the pace & style of expansion.
Election speeches are brought back from prior entries, as I understand it, and don't seem terribly notable.
While the monument-stealing is stylistically too goofy for my tastes, in terms of mechanics I think it's done well. Each era has a small selection to pick from with significant effects, but you only get to pick one from each era.
On the whole, I feel like it strikes a nice balance between the 'no worries, just relax' city builders and the 'tough as nails' city builders out there.
My only concern -- which isn't well-researched, just an impression I have -- is that heavy industrialization was the only way to keep the economy afloat. My attempts at tourism have been moneypits, and focusing on less polluting (less advanced) industry didn't bring in enough money starting in the cold war era. I'm planning on spending more time with it once the 1.0 is actually out. [edit: looks like it's actually out now, whoops].