I put in 6 straight hours last night, but I'm undecided if I really like the direction they went with Tropico 5. While the base game is much the same, many of the mechanics have changed. Didn't try multiplayer yet.
You can't 'buy plans' for buildings anymore, but have to research buildings (and edicts, etc), and have to be in the right Era (colonial, cold war, etc). What this does, is highly restricts what you can build, so early game you have hardly any buildings at all to construct. Not liking that so much, except you end up using buildings you may have skipped over before like regular Houses. Many buildings now have secondary attributes, like the regular House increasing in quality the more houses you have around it.
Every production type building can now have a manager, and there are varieties like General that increases military buildings, and Environmentalist that decreases pollution in all buildings around. This I do like, as it adds new strategy. You also can have children now, and your children can be managers, or can be elected to your job.
Combat is almost RTS like, but with a Total War type of feel (units are a group). But, it's pretty much automatic, so don't get your hopes up for a true mix of RTS and Tropico.
Importing resources is gone as it was, and instead there are now trade routes. You assign ships to contracts like 10 years of shipping Corn to Allies at a set price. I like this better, as ships are limited, so you can't just import all raw materials and have an island of factories.
I'm on the sixth campaign mission, and have only seen two islands. Every other mission, you return to a previous island, along with everything you already built on it in previous missions. I really do not like this repeating island thing... rather have a new island for every mission, although I might like the carryover later on. Right now if the campaign is 15 missions, you are looking at a whole 5 maps total... hope that is not the case.
Overall pretty happy with it. Enough new mechanics that it changes the way you play (it isn't Tropico 3.5.5), but some things I don't like so far.