My Indonesia Review:
Indonesia is a very powerful civ, particularly on Island Plates maps that play to its strengths.
Great Nusantara:
Having an adjacency bonus to coastal tiles is part of Indonesia's coastal focus. In many cases, these districts would be better suited inland, but this bonus makes them viable when placed on the coast. On IP maps, you may not have a choice otherwise. The extra amenity on the Entertainment Complex is more important than expected, because you are going to have some astoundingly large cities. Indonesia's Theater Squares are one of the few with an actual terrain adjacency bonus (Brazil and Australia have the others).
Exalted Goddess of the Three Worlds:
The free Faith in coastal cities is very helpful for gaining first pick on Pantheons. Most likely you will be getting God of the Sea for that sweet, sweet sea resource production. It's somewhat less useful for buying units with Faith, because it doesn't add up that fast. If you are planning to Faith-purchase a huge navy, this will need to be supplemented with Faith from Holy Sites and religion. But if you're just occasionally buying caravels, it's probably fine.
I don't play towards religious victories, but I can see how having your missionaries sweep in off the sea and blitz cities with conversion is pretty powerful, as that would be hard to defend against.
Jong
The Jong is faster, stronger (with an accompanying embarked land unit), and comes a whole era earlier than the Frigate that it replaces. I was attacked by the Greeks who got Caravels before I did, but I got my Jongs and ripped them apart. It helps that Mercenaries is relatively easy to beeline. The downside is that you will have to invest a little bit more production to get a land unit to ride on it, to get its full potential.
Kampung
The Outback Station of the sea! And like that improvement, you will be spamming Kampungs anywhere you can because there's no reason not to. The yields are good, especially when you get a Lighthouse up (and later a Seaport). The Housing is simply ridiculous for an improvement that you could have 10 or more per city. It starts with 1 Housing, and then gets another 1 at Square Rigging! Either that second one needs to be moved to later in the tech tree or it needs to be reduced to half. I expect it to be nerfed in a future patch. And if making huge cities wasn't enough, these things also generate Tourism at Flight, despite having no Culture. I haven't figured out if the Tourism is equivalent to the Food generated or what, but they increased my raw Tourism index by 75%. So, they are kind of a cross between the Outback Station and the Pairediazas.
The downside of coastal improvements and districts is that a band of naval raiders (I'm looking at England and Norway here) could sweep in and lay waste to your infrastructure. Be sure to keep a strong navy in defense.
TL;DR Indonesia is really good on any map with water, and breathtaking on Island Plates.