Foz has two major sights: perhaps the most stunning collection of waterfalls in the world and the second biggest dam in the world. Like Victoria Falls, Iguaçu Falls can be visited from both sides, here Brazilian and Argentinian. If you don't suffer for reciprocated visa fees, like Americans do, going over to Argentina is a breeze, where the Argentinian side of the river feels much more provincial than the Brazilian side. The town of Foz de Iguaçu, on the Brazilian side, is not too interesting either, for its generic characteristics, but at least there's an energetic bustle. On the other side of the river, Puerto Iguazu feels almost comatose.
The falls are impressive, but it's hard to say whether they steal the limelight from Victoria Falls. At least here, the infrastructure is in great condition, while the crowds weren't too bad. And I didn't get soaked, which might be seasonal.
Visiting Itaipu dam, though, is underwhelming. Visiting, you're put on a bus and get to leave the bus during two short visits, allowing you to take photos of the dam in the distance. You also drive over the dam, but this doesn't give you a good impression of the sheer size of the dam, nor does it allow for good photo opportunities.